refactor(combined_main): remove P2P placeholder and improve shutdown handling

- Remove P2P placeholder server integration
- Add global service instance for signal handlers
- Add set_stop_event method for clean shutdown
- Improve signal handler to properly trigger stop event
- Store event loop reference for shutdown coordination
- Update logging to reflect P2P removal

apps/blockchain-node/src/aitbc_chain/combined_main.py

@@ -15,7 +15,6 @@ from pathlib import Path
 sys.path.insert(0, str(Path(__file__).parent.parent))
 
 from aitbc_chain.main import BlockchainNode, _run as run_node
-from aitbc_chain.p2p_placeholder import run_server as run_p2p_server
 from aitbc_chain.config import settings
 
 logging.basicConfig(level=logging.INFO)
@@ -25,22 +24,23 @@ class CombinedService:
     def __init__(self):
         self._stop_event = asyncio.Event()
         self._tasks = []
+        self._loop = None
+        
+    def set_stop_event(self):
+        """Set the stop event to trigger shutdown"""
+        if self._stop_event and not self._stop_event.is_set():
+            self._stop_event.set()
         
     async def start(self):
         """Start both blockchain node and P2P server"""
+        self._loop = asyncio.get_running_loop()
         logger.info("Starting combined blockchain service")
         
-        # Start P2P server
-        p2p_task = asyncio.create_task(
-            run_p2p_server(settings.p2p_bind_host, settings.p2p_bind_port)
-        )
-        self._tasks.append(p2p_task)
-        
         # Start blockchain node in background
         node_task = asyncio.create_task(run_node())
         self._tasks.append(node_task)
         
-        logger.info(f"Combined service started - P2P on {settings.p2p_bind_host}:{settings.p2p_bind_port}, Node on mainnet")
+        logger.info(f"Combined service started - Node on mainnet")
         
         try:
             await self._stop_event.wait()
@@ -62,14 +62,21 @@ class CombinedService:
         self._tasks.clear()
         logger.info("Combined service stopped")
 
+# Global service instance for signal handler
+_service_instance = None
+
 def signal_handler(signum, frame):
     """Handle shutdown signals"""
     logger.info(f"Received signal {signum}, initiating shutdown")
-    # The event will be checked in the main loop
+    global _service_instance
+    if _service_instance:
+        _service_instance.set_stop_event()
 
 async def main():
     """Main entry point"""
+    global _service_instance
     service = CombinedService()
+    _service_instance = service
     
     # Set up signal handlers
     signal.signal(signal.SIGTERM, signal_handler)
@@ -81,6 +88,7 @@ async def main():
         logger.info("Received keyboard interrupt")
     finally:
         await service.stop()
+        _service_instance = None
 
 if __name__ == "__main__":
     asyncio.run(main())