fix: add MCP server ready check to prevent initialization errors

Add server ready state tracking for MCP service to prevent
"Received request before initialization was complete" errors
when clients connect before GNS3 server completes startup.

Changes:
- Add MCP server ready state management with wait/notify mechanism
- Modify auth wrapper to wait for server initialization before accepting connections
- Set MCP server ready flag after GNS3 startup completes

This ensures MCP protocol initialization handshake only occurs
after GNS3 server is fully initialized, preventing race
conditions during server startup.

gns3server/core/tasks.py

@@ -84,6 +84,11 @@ async def startup(app: FastAPI) -> None:
         m = module.instance()
         m.port_manager = PortManager.instance()
 
+    # Mark MCP server as ready to accept connections
+    from gns3server.api.routes.mcp import set_mcp_server_ready
+    set_mcp_server_ready(True)
+    log.info("GNS3 server startup completed")
+
 
 async def shutdown(app: FastAPI) -> None:
     """