feat(channels): add multi-channel management UI with real-time connect/disconnect

- Web console Channels page: display active channels as config cards, support
  save/connect/disconnect with real-time start/stop of channel processes
- Custom dropdown for channel selection (consistent with model selector style),
  custom confirmation dialog for disconnect
- Fix channel stop: use sys.modules['__main__'] to access live ChannelManager
- Fix web request pending: move stop logic outside lock, set daemon_threads=True
- Fix reconnect: new asyncio event loop per startup, ctypes thread interrupt,
  5s grace period before re-establishing remote connection
- Filter stale offline messages (>60s) pushed after reconnect

bridge/agent_initializer.py

@@ -145,7 +145,7 @@ class AgentInitializer:
             # after a restart.  The full max_turns budget is reserved for the
             # live conversation that follows.
             max_turns = conf().get("agent_max_context_turns", 30)
-            restore_turns = min(6, max(1, max_turns // 3))
+            restore_turns = max(4, max_turns // 5)
             saved = store.load_messages(session_id, max_turns=restore_turns)
             if saved:
                 with agent.messages_lock: