[management, client, proxy] Follow-up fixes for private reverse-proxy services (#6268)

* fix(proxy): gate tunnel-peer fast-path on inbound listener marker

forwardWithTunnelPeer previously accepted any RFC1918 / ULA / CGNAT
source IP, so a public client whose address happened to fall in those
ranges could bypass the configured operator auth scheme by colliding
with a known tunnel IP. The fast-path is now gated on
TunnelLookupFromContext(r.Context()) being present — that context value
is attached only by the per-account inbound (overlay) listener, so the
host-facing listener never enters this branch.

Tests updated to reflect the new requirement: requests that don't
carry the inbound marker now fall through to the regular auth flow.

* fix(proxy): harden inbound listener resource + startup-ctx handling

Three correctness fixes on the per-account inbound path, with tests:

- Close the logrus ErrorLog PipeWriter on tearDown. WriterLevel hands
  back an *io.PipeWriter backed by a pipe + scanner goroutine that the
  caller owns; the two writers per account (https + plain) were never
  closed, leaking the pipe and goroutine on every teardown.
- Run the post-Start hooks on context.Background(). runClientStartup
  is launched in a goroutine from AddPeer and was inheriting the
  caller's request-scoped ctx, so a cancelled request could abort the
  inbound bring-up or fail the management status notification. The
  tail is split into notifyClientReady so the contract is testable.

Tests cover the PipeWriter close behaviour and assert the readyHandler
+ NotifyStatus calls receive a non-cancelled background context.

* feat(proxy): short-circuit peer-own-target loops with 421

When a peer that hosts the target of a private service dials its own
service URL the request was being looped through the proxy and back
over WireGuard to the same peer — twice the WG round-trip for no
benefit, with no signal to the caller that something was wrong.

Add isSelfTargetLoop to ReverseProxy.ServeHTTP: when the request
arrived on the per-account overlay listener (IsOverlayOrigin) and the
source tunnel IP matches the target host, refuse the request with 421
Misdirected Request and a body pointing the operator at the backend
directly.

The gate is scoped to overlay origin so requests on the public
listener that happen to share a source IP with the target host are
forwarded normally.

* fix(management): private-service validation + tunnel-IP lookup semantics

- Require an explicit port for L4 cluster targets. validateL4Target
  exempted TargetTypeCluster from the port check, but buildPathMappings
  serializes every L4 target via net.JoinHostPort(host, port) — port=0
  shipped a ":0" upstream. Cluster targets use the same Host/Port
  fields, so the same requirement applies.
- GetPeerByIP returns NotFound on a tunnel-IP miss instead of mapping
  every error to Internal. The proxy's ValidateTunnelPeer probes IPs
  that legitimately aren't in the roster; the miss is expected and now
  distinguishable from a real store failure.
- Thread ctx into getClusterCapability's gorm query so a cancelled
  request doesn't keep the store busy.

Tests updated for the L4-cluster port requirement and the GetPeerByIP
NotFound path.

* fix(client): include offlinePeers in PeerStateByIP lookup

ReplaceOfflinePeers moves peers into d.offlinePeers but PeerStateByIP
only scanned d.peers. Callers (the local DNS filter via
localPeerConnectivity, embed.Client.IdentityForIP used by the
proxy's tunnel-peer validator) were treating known-but-offline peers
as unknown, which:

- causes the DNS filter to keep returning records pointing at peers
  that have no live tunnel, AND
- makes the proxy's local-roster check deny a request from such a
  peer rather than letting the cached management RPC carry the
  authorisation decision.

Search both slices in PeerStateByIP. Adds a unit test for the IPv4
and IPv6 offline-match paths.

* fix(rest): reject empty Delete path params in reverse-proxy clients

ReverseProxyClustersAPI.Delete and ReverseProxyTokensAPI.Delete passed
the path parameter into url.PathEscape without an empty check.
PathEscape("") returns "" which collapses the request onto the
collection endpoint ("/api/reverse-proxies/clusters/" /
"/api/reverse-proxies/proxy-tokens/"), so a caller bug delete with no
id reached a routable URL with surprising semantics (typically 405).

Short-circuit with a typed error before the request is built. Tests
mount a handler on the collection path that fails the test if hit, so
the regression is impossible to reintroduce silently.

* chore(api,ci,docs,test): private-service schema, proto-check, fixups

Non-functional cleanups and contract/CI hardening around the
private-service work:

API schema (openapi.yml):
- Require a non-empty access_groups and mode=http when private=true,
  on both Service and ServiceRequest, mirroring
  validatePrivateRequirements. mode stays optional-but-constrained
  (empty defaults to http server-side), matching runtime.

CI (proto-version-check.yml):
- Cover renamed .pb.go files (read base via previous_filename).
- Match protoc-gen-go-grpc version headers (optional "- " prefix and
  -gen-go-grpc suffix) so grpc-generated files are in scope.

Docs / comments:
- Reword Config field docs to say defaults are applied at Server.Start
  (initDefaults), not New.
- Rename the obsolete --private-inbound flag to --private across
  comments and the proto doc.

Pre-existing test fixups surfaced by review:
- Repair the integration-tagged validate_session_test.go (SignToken
  signature growth + new Manager interface methods).
- Fix the CI-skip boolean precedence so Windows isn't skipped
  unconditionally.
- Guard the router.HTTPListener type assertion with comma-ok.

* fix(proxy): background ctx for already-started AddPeer notification

The earlier ctx fix covered the async runClientStartup path but missed
the synchronous branch: when a service is added to an already-started
client, AddPeer called NotifyStatus with the caller's request-scoped
ctx. A cancelled request/stream could drop the connected notification
to management. Use context.Background() here too, matching
notifyClientReady.

Extends TestNetBird_AddPeer_ExistingStartedClient_NotifiesStatus to
pass a pre-cancelled caller ctx and assert the notification still ran
on a non-cancelled context.

* use the cmd context for roundtripper

proxy/internal/auth/middleware.go

@@ -346,13 +346,15 @@ func (mw *Middleware) forwardWithSessionCookie(w http.ResponseWriter, r *http.Re
 // management unreachable, peer unknown, user not in group) returns false so
 // the caller falls back to the existing OIDC scheme dispatch.
 //
-// Phase 3 adds a local-first short-circuit: when the request arrived on a
-// per-account inbound listener the context carries a peerstore lookup
-// (TunnelLookupFromContext). If the lookup says the IP isn't in the account's
-// roster the proxy denies fast without calling management. If the lookup
-// confirms a known peer the RPC still runs for the user-identity tail
-// (UserID + group access), but its result is cached for tunnelCacheTTL so
-// repeat requests skip management entirely.
+// The fast-path is gated on TunnelLookupFromContext(r.Context()) being
+// present — that context value is attached only by the per-account
+// inbound (overlay) listener. The host listener never sets it, so a
+// public client whose source IP happens to fall inside an RFC1918 / ULA
+// / CGNAT range can't impersonate a mesh peer by colliding with a
+// tunnel-IP. Once we know the request arrived over WireGuard the
+// per-account peerstore lookup is consulted: a miss denies fast (no
+// management round-trip), a hit gates the cached ValidateTunnelPeer RPC
+// that mints the session JWT.
 func (mw *Middleware) forwardWithTunnelPeer(w http.ResponseWriter, r *http.Request, host string, config DomainConfig, next http.Handler) bool {
 	if mw.sessionValidator == nil {
 		return false
@@ -361,18 +363,24 @@ func (mw *Middleware) forwardWithTunnelPeer(w http.ResponseWriter, r *http.Reque
 	if !clientIP.IsValid() {
 		return false
 	}
+
+	// Anti-spoof: only honour the tunnel-peer fast-path on requests that
+	// were stamped by an overlay listener. Without that marker an
+	// attacker could send a request from a colliding RFC1918 / CGNAT
+	// source on the public listener and bypass operator auth.
+	lookup := TunnelLookupFromContext(r.Context())
+	if lookup == nil {
+		return false
+	}
 	if !isTunnelSourceIP(clientIP) {
 		return false
 	}
-
-	if lookup := TunnelLookupFromContext(r.Context()); lookup != nil {
-		if _, ok := lookup(clientIP); !ok {
-			mw.logger.WithFields(log.Fields{
-				"host":   host,
-				"remote": clientIP,
-			}).Debug("local peerstore: tunnel IP not in account roster; denying without RPC")
-			return false
-		}
+	if _, ok := lookup(clientIP); !ok {
+		mw.logger.WithFields(log.Fields{
+			"host":   host,
+			"remote": clientIP,
+		}).Debug("local peerstore: tunnel IP not in account roster; denying without RPC")
+		return false
 	}
 
 	resp, _, err := mw.tunnelCache.fetch(r.Context(), tunnelCacheKey{