fix: make gateway watcher startup non-blocking with timeout (#4297)

start_watcher() ran synchronously in main() at boot; if
_resolve_watcher_target() blocked (locked state.db, slow profile
resolution, I/O stall) the server never bound its port — a startup
brick. Run it on a daemon thread with a 5s join so boot proceeds even
if watcher init stalls; the poll loop already runs on its own daemon
thread so liveness is unchanged.

Co-authored-by: minidarkmimi <minidarkmimi@users.noreply.github.com>

server.py

@@ -593,7 +593,18 @@ def main() -> None:
     # Start the gateway session watcher for real-time SSE updates
     try:
         from api.gateway_watcher import start_watcher
-        start_watcher()
+
+        def _start_watcher_safe():
+            try:
+                start_watcher()
+            except Exception as e:
+                print(f'[!!] WARNING: Gateway watcher failed to start: {e}', flush=True)
+
+        t = threading.Thread(target=_start_watcher_safe, daemon=True)
+        t.start()
+        t.join(timeout=5)
+        if t.is_alive():
+            print('[tip] Gateway watcher still initializing (non-blocking)', flush=True)
     except Exception as e:
         print(f'[!!] WARNING: Gateway watcher failed to start: {e}', flush=True)