feat(gateway): deliver background review notifications to user chat (#3293)

The background memory/skill review (_spawn_background_review) runs
after the agent response when turn/iteration counters exceed their
thresholds. It saves memories and skills, then prints a summary like
'💾 Memory updated · User profile updated'. In CLI mode this goes to
the terminal via _safe_print. In gateway mode, _safe_print routes to
print() which goes to stdout — invisible to the user.

Add a background_review_callback attribute to AIAgent. When set, the
background review thread calls it with the summary string after saves
complete. The gateway wires this to adapter.send() via the same
run_coroutine_threadsafe bridge used by status_callback, delivering
the notification to the user's chat.

gateway/run.py

@@ -5128,7 +5128,25 @@ class GatewayRunner:
             agent.stream_delta_callback = _stream_delta_cb
             agent.status_callback = _status_callback_sync
             agent.reasoning_config = reasoning_config
-            
+
+            # Background review delivery — send "💾 Memory updated" etc. to user
+            def _bg_review_send(message: str) -> None:
+                if not _status_adapter:
+                    return
+                try:
+                    asyncio.run_coroutine_threadsafe(
+                        _status_adapter.send(
+                            _status_chat_id,
+                            message,
+                            metadata=_status_thread_metadata,
+                        ),
+                        _loop_for_step,
+                    )
+                except Exception as _e:
+                    logger.debug("background_review_callback error: %s", _e)
+
+            agent.background_review_callback = _bg_review_send
+
             # Store agent reference for interrupt support
             agent_holder[0] = agent
             # Capture the full tool definitions for transcript logging