android: utun shutdown diagnostics + non-blocking stop + logreceiver doc

- instance_lite: cleanup moved to uasync thread (self-detach), events on start/stop
- udp_log: cancel_timer before uasync_destroy, flush on stop, stopping flag
- jni_bridge: fixed UDP stop order (cancel_timer → destroy → flush)
- instance_lite: u_report_unfreed_blocks at all shutdown paths
- chat_event: CHAT_EVT_SERVICE_STARTED/STOPPED for GUI notifications
- AGENTS: logreceiver section

src/chat/chat_event.h

@@ -30,6 +30,8 @@ extern "C" {
 #define CHAT_EVT_DB_READY            9   /* data: none */
 #define CHAT_EVT_STATUS_REFRESH     10   /* data: status text */
 #define CHAT_EVT_KEYS_GENERATED     11   /* [pub_hex:64] */
+#define CHAT_EVT_SERVICE_STARTED    12   /* data: none */
+#define CHAT_EVT_SERVICE_STOPPED    13   /* data: none */
 
 typedef void (*chat_event_handler_fn)(int type, const uint8_t* data, int len);