Add web server error handling and proper shutdown

- Add stop() method to WebServer class
- Store server instance for graceful shutdown
- Add error handling in start_server() with user-friendly alert
- Show warning dialog if server fails to start (e.g., port in use)
- Stop server in closeEvent before application exit
- Add status bar messages for server state

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

gui/main_window.py

@@ -330,14 +330,48 @@ class MainWindow(QMainWindow):
 
     def start_server(self):
         """Start the web server in a background thread."""
-        self.web_server.create_app()
+        self.server_error = None
 
         def run():
-            self.web_server.run()
+            try:
+                self.web_server.create_app()
+                self.web_server.run()
+            except Exception as e:
+                self.server_error = str(e)
+                # Emit signal to show error on main thread
+                QTimer.singleShot(0, self.show_server_error)
 
         self.server_thread = threading.Thread(target=run, daemon=True)
         self.server_thread.start()
-        self.status_bar.showMessage(f"Server running on port {DEFAULT_PORT}")
+
+        # Give the server a moment to start, then check for errors
+        QTimer.singleShot(1000, self.check_server_started)
+
+    def check_server_started(self):
+        """Check if server started successfully."""
+        if self.server_error:
+            self.show_server_error()
+        else:
+            self.status_bar.showMessage(f"Server running on port {DEFAULT_PORT}")
+
+    def show_server_error(self):
+        """Show server error dialog."""
+        error_msg = self.server_error or "Unknown error"
+        self.status_bar.showMessage(f"Server failed to start")
+        QMessageBox.warning(
+            self,
+            "Web Server Error",
+            f"Failed to start web server on port {DEFAULT_PORT}.\n\n"
+            f"Error: {error_msg}\n\n"
+            "The web interface will not be available.\n"
+            "Check if another application is using the port."
+        )
+
+    def stop_server(self):
+        """Stop the web server."""
+        if self.web_server:
+            self.web_server.stop()
+        self.status_bar.showMessage("Server stopped")
 
     def update_ip_label(self):
         """Update the IP address label."""
@@ -510,7 +544,12 @@ class MainWindow(QMainWindow):
 
     def closeEvent(self, event):
         """Handle window close."""
+        # Stop the web server
+        self.stop_server()
+
+        # Hide tray icon
         self.tray_icon.hide()
+
         event.accept()
 
     def resizeEvent(self, event):

web_server.py

@@ -254,8 +254,13 @@ class WebServer:
             port=self.port,
             log_level="warning"
         )
-        server = uvicorn.Server(config)
+        self.server = uvicorn.Server(config)
-        server.run()
+        self.server.run()
+
+    def stop(self):
+        """Stop the web server."""
+        if self.server:
+            self.server.should_exit = True
 
     async def run_async(self):
         """Run the web server asynchronously."""