[client] Provision the peer identity on the iOS login path

Key generation used to happen inside apply(), so a config loaded from JSON with
no keys got them in memory on the way in, the login worked, and the app stored
the result. This branch moved generation into EnsureIdentity, and nothing in
the iOS SDK called it.

The consequence lands on the flow the mobile logout sets up: logout clears both
keys in place so the next login registers a new peer. The app then hands that
keyless JSON to Auth.SetConfigFromJSON, and the login calls auth.NewAuth with
an empty WireGuard key, which fails on key size before the SSO flow starts —
the user cannot sign back in.

Auth.setBaseConfig now provisions, which covers both entry points (NewAuth and
SetConfigFromJSON). It mints on the base config, the one GetConfigJSON returns
for the caller to persist, and writes it to disk itself when the profile has a
file — non-atomically, like NewAuth's own write, since the tvOS App Group
sandbox blocks temp-file-and-rename.

Not covered by a test: the package builds only under GOOS=ios, which the test
jobs do not run. Verified by building and vetting for GOOS=ios/arm64.

Reported by pappz in review.

client/ios/NetBirdSDK/login.go

@@ -379,6 +379,35 @@ func (a *Auth) SetConfigFromJSON(jsonStr string) error {
 }
 
 func (a *Auth) setBaseConfig(base *profilemanager.Config) error {
+	// A logged-out profile carries no keys: the mobile logout clears them in
+	// place so the next login registers a new peer instead of resurrecting the
+	// old one. This is that login, and auth.NewAuth parses the WireGuard key
+	// before the SSO flow even starts, so an absent identity fails the login on
+	// key size rather than asking the user to sign in.
+	//
+	// Minted on the base config, which is the one GetConfigJSON hands back for
+	// the caller to store — the overlaid copy below is runtime-only.
+	generated, err := base.EnsureIdentity()
+	if err != nil {
+		return fmt.Errorf("ensure profile identity: %w", err)
+	}
+	if generated {
+		if a.cfgPath != "" {
+			// Non-atomic, like NewAuth's own write: the tvOS App Group sandbox
+			// blocks the temp-file-and-rename an atomic write needs.
+			if err := profilemanager.DirectWriteOutConfig(a.cfgPath, base); err != nil {
+				return fmt.Errorf("write out profile config: %w", err)
+			}
+		} else {
+			// No file to write to — this is the tvOS path, where the profile
+			// lives in the caller's own store. It persists the new identity by
+			// calling GetConfigJSON once the login completes; until then the
+			// keys exist only here, and a login that never completes leaves
+			// nothing behind.
+			log.Infof("provisioned a peer identity for a config with no file on disk")
+		}
+	}
+
 	overlaid, err := copyConfig(base)
 	if err != nil {
 		return err