[client] iOS - Remove duplicate Login RPCs from the iOS SDK (#6931)

## Describe your changes

Removes redundant `Login` RPCs from the iOS SDK bindings.

## Issue ticket number and link

## Stack

<!-- branch-stack -->

### Checklist
- [x] Is it a bug fix
- [ ] Is a typo/documentation fix
- [ ] Is a feature enhancement
- [ ] It is a refactor
- [ ] Created tests that fail without the change (if possible)
- [ ] This change does **not** modify the public API, gRPC protocols,
functionality behavior, CLI / service flags, or introduce a new feature
— **OR** I have discussed it with the NetBird team beforehand (link the
issue / Slack thread in the description). See
[CONTRIBUTING.md](https://github.com/netbirdio/netbird/blob/main/CONTRIBUTING.md#discuss-changes-with-the-netbird-team-first).

> By submitting this pull request, you confirm that you have read and
agree to the terms of the [Contributor License
Agreement](https://github.com/netbirdio/netbird/blob/main/CONTRIBUTOR_LICENSE_AGREEMENT.md).

## Documentation
Select exactly one:

- [ ] I added/updated documentation for this change
- [x] Documentation is **not needed** for this change (explain why)

### Docs PR URL (required if "docs added" is checked)
Paste the PR link from https://github.com/netbirdio/docs here:

https://github.com/netbirdio/docs/pull/__

<!-- codesmith:footer -->
---
<a
href="https://app.blacksmith.sh/netbirdio/codesmith/netbird/pr/6931"><picture><source
media="(prefers-color-scheme: dark)"
srcset="https://pr-comments-assets.blacksmith.sh/codesmith/view-with-codesmith-dark-v2.svg"><source
media="(prefers-color-scheme: light)"
srcset="https://pr-comments-assets.blacksmith.sh/codesmith/view-with-codesmith-light-v2.svg"><img
alt="View with [code]smith"
src="https://pr-comments-assets.blacksmith.sh/codesmith/view-with-codesmith-dark-v2.svg"></picture></a>
<a
href="https://backend.blacksmith.sh/track/enable-autofix?expires=1787779607&installation_model_id=427504&pr_number=6931&repository=netbirdio%2Fnetbird&return_to=https%3A%2F%2Fgithub.com%2Fnetbirdio%2Fnetbird%2Fpull%2F6931&signature=ce1631be2a5ffdba58c44b4669b0d480dc9f956102cf10a0c7b5845a800cdc68"><picture><source
media="(prefers-color-scheme: dark)"
srcset="https://pr-comments-assets.blacksmith.sh/codesmith/autofix-with-codesmith-dark.svg"><source
media="(prefers-color-scheme: light)"
srcset="https://pr-comments-assets.blacksmith.sh/codesmith/autofix-with-codesmith-light.svg"><img
alt="Autofix with [code]smith"
src="https://pr-comments-assets.blacksmith.sh/codesmith/autofix-with-codesmith-dark.svg"></picture></a>
<sup>Need help on this PR? Tag <code>@codesmith-bot</code> with what you
need. Autofix is disabled.</sup>

<!-- codesmith:autofix:disabled -->
<!-- /codesmith:footer -->

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->

## Summary by CodeRabbit

* **New Features**
* Added an interactive iOS login option that starts authentication
directly when needed.
* Improved login flow handling, including clearer error reporting and
successful-login notifications.
* Login configuration is now saved automatically after successful
authentication when applicable.

* **Bug Fixes**
  * Prevented duplicate login requests during iOS startup.
* Improved startup behavior and error propagation when the management
service is unavailable.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->


Removes redundant `Login` RPCs from the iOS SDK bindings. Both changed
files are behind
the `ios` build tag — Android, desktop and the shared core are not
affected.

### Problem

`auth.Auth.IsLoginRequired()` is not a cheap probe: it calls
`doMgmLogin()` and classifies
the resulting error, so every "is login required?" check costs a **full
`Login` RPC**. There
is no lighter way to ask. As a result the iOS client issued ~7 `Login`
requests before the
first `Sync`, where Android issues ~3, and the extra ones were
indistinguishable from real
logins in the management logs.

Three of those came from this package:

1. `Run()` called `LoginSync()` before starting the engine, which
performs `IsLoginRequired`
**and** `Login` — two RPCs. This duplicated the engine's own
`loginToManagement`
(`client/internal/connect.go`), which runs immediately before the first
`Sync` and is the
authoritative login. The `Login(ctx, "", "")` inside `LoginSync` could
not even establish
anything: with an empty setup key and empty JWT, a registration attempt
fails by
   construction, so it was a pure check.
2. `Auth.login()` called `IsLoginRequired()` again before opening the
browser, even when the
   caller had already determined that login is needed.

This is not only wasted traffic:

- **It pushes peers toward the server-side login ban.** In
`management/internals/shared/grpc/loginfilter.go`, every login with
unchanged metadata
increments `sessionCounter`, and exceeding `reconnLimitForBan` (30)
within
`reconnThreshold` (5 min) bans the peer for `baseBlockDuration` (10
min), doubling on
repeat. Redundant logins carry identical metadata, so they count against
exactly this
budget. At 7 logins per connect the budget is exhausted after ~4
reconnects instead of
  ~10 — reachable on flaky mobile networks.
- **Each redundant check is a potential 2-minute stall.**
`IsLoginRequired` retries with
backoff up to `MaxElapsedTime` (2 min) and returns `true` on failure, so
an unreachable
server was reported as "login required" rather than as a timeout, and
the `LoginSync`
  pre-flight could abort engine startup on that basis.

### Changes

**`client/ios/NetBirdSDK/client.go`** — `Run()` no longer performs the
`LoginSync()`
pre-flight. The engine's `loginToManagement` remains the single
authoritative login.

**`client/ios/NetBirdSDK/login.go`** — new exported `LoginInteractive`,
which skips the
`IsLoginRequired()` pre-flight and goes straight to the browser /
device-code flow, for
callers that have already established login is required.
`LoginWithDeviceName` keeps the
check for callers where the auth state is unknown (tvOS). Both now
delegate to a shared
`startLogin()`.

### Why this is safe

An expired or revoked session still fails the connection, one step later
and through a
single path: `loginToManagement` returns `PermissionDenied` → the
deferred
`MarkManagementDisconnected` records it on the shared status recorder →
`ClientStop` fires
the listener's disconnect callback, where `IsLoginRequiredCached()`
reports login-required →
the client tears the tunnel down. The error is also returned out of
`Run()`.

Where the server is unreachable, the engine now retries with backoff and
recovers on its
own instead of aborting the start.

Co-authored-by: Zoltan Papp <zoltan.pmail@gmail.com>

client/ios/NetBirdSDK/client.go

@@ -158,13 +158,19 @@ func (c *Client) Run(fd int32, interfaceName string, envList *EnvList) error {
 	defer c.ctxCancel()
 	c.ctxCancelLock.Unlock()
 
-	auth := NewAuthWithConfig(ctx, cfg)
-	err = auth.LoginSync()
-	if err != nil {
-		return err
-	}
-
-	log.Infof("Auth successful")
+	// No login pre-flight here. The engine's own loginToManagement (connect.go) performs
+	// the authoritative Login immediately before the first Sync, so a LoginSync() call at
+	// this point only duplicated it — costing two extra Login RPCs (IsLoginRequired +
+	// Login) on every engine start, since IsLoginRequired is itself a full Login RPC.
+	//
+	// Auth failures still reach the caller through the engine path: loginToManagement
+	// returns PermissionDenied, which marks the shared status recorder
+	// (MarkManagementDisconnected) and fires ClientStop → onDisconnected, where
+	// IsLoginRequiredCached() reports login-required. The error is also returned out of Run().
+	//
+	// A pre-flight was also actively harmful when the server is unreachable: its 2-minute
+	// backoff blocked the start and then reported "login required" for what was really a
+	// timeout. The engine instead keeps retrying and recovers when the server returns.
 	// todo do not throw error in case of cancelled context
 	ctx = internal.CtxInitState(ctx)
 	c.onHostDnsFn = func([]string) {}

client/ios/NetBirdSDK/login.go

@@ -222,17 +222,36 @@ func (a *Auth) Login(resultListener ErrListener, urlOpener URLOpener, forceDevic
 // LoginWithDeviceName performs interactive login with device authentication support
 // The deviceName parameter allows specifying a custom device name (required for tvOS)
 func (a *Auth) LoginWithDeviceName(resultListener ErrListener, urlOpener URLOpener, forceDeviceAuth bool, deviceName string) {
+	a.startLogin(resultListener, urlOpener, forceDeviceAuth, deviceName, false)
+}
+
+// LoginInteractive performs the same interactive login as LoginWithDeviceName but skips the
+// IsLoginRequired() pre-flight and goes straight to the browser / device-code flow.
+//
+// IsLoginRequired() is itself a full Login RPC against the management server, so when the
+// caller has ALREADY established that login is required it is a pure duplicate. On iOS the
+// main app decides to show the browser based on its own isLoginRequired() check and then
+// calls straight into this method, so re-asking the server would add another Login RPC to
+// every interactive login.
+//
+// Use LoginWithDeviceName when the auth state is unknown and a silent (browser-less) login
+// must still be possible; use this when the browser is going to be shown regardless.
+func (a *Auth) LoginInteractive(resultListener ErrListener, urlOpener URLOpener, forceDeviceAuth bool, deviceName string) {
+	a.startLogin(resultListener, urlOpener, forceDeviceAuth, deviceName, true)
+}
+
+func (a *Auth) startLogin(resultListener ErrListener, urlOpener URLOpener, forceDeviceAuth bool, deviceName string, skipLoginCheck bool) {
 	if resultListener == nil {
-		log.Errorf("LoginWithDeviceName: resultListener is nil")
+		log.Errorf("startLogin: resultListener is nil")
 		return
 	}
 	if urlOpener == nil {
-		log.Errorf("LoginWithDeviceName: urlOpener is nil")
+		log.Errorf("startLogin: urlOpener is nil")
 		resultListener.OnError(fmt.Errorf("urlOpener is nil"))
 		return
 	}
 	go func() {
-		err := a.login(urlOpener, forceDeviceAuth, deviceName)
+		err := a.login(urlOpener, forceDeviceAuth, deviceName, skipLoginCheck)
 		if err != nil {
 			resultListener.OnError(err)
 		} else {
@@ -241,7 +260,7 @@ func (a *Auth) LoginWithDeviceName(resultListener ErrListener, urlOpener URLOpen
 	}()
 }
 
-func (a *Auth) login(urlOpener URLOpener, forceDeviceAuth bool, deviceName string) error {
+func (a *Auth) login(urlOpener URLOpener, forceDeviceAuth bool, deviceName string, skipLoginCheck bool) error {
 	// Create context with device name if provided
 	ctx := a.ctx
 	if deviceName != "" {
@@ -255,10 +274,13 @@ func (a *Auth) login(urlOpener URLOpener, forceDeviceAuth bool, deviceName strin
 	}
 	defer authClient.Close()
 
-	// check if we need to generate JWT token
-	needsLogin, err := authClient.IsLoginRequired(ctx)
-	if err != nil {
-		return fmt.Errorf("failed to check login requirement: %v", err)
+	// check if we need to generate JWT token (skipped when the caller already knows)
+	needsLogin := true
+	if !skipLoginCheck {
+		needsLogin, err = authClient.IsLoginRequired(ctx)
+		if err != nil {
+			return fmt.Errorf("failed to check login requirement: %v", err)
+		}
 	}
 
 	jwtToken := ""