fix: close per-request server and transport in example-apps handler

The stateless /:slug/mcp handler creates a fresh McpServer and
StreamableHTTPServerTransport on every request but never closed them,
leaking memory under load. Register a 'close' listener (fires on both
normal completion and client abort mid-SSE) to release them.

src/modules/example-apps/index.ts

@@ -133,6 +133,11 @@ export class ExampleAppsModule {
           sessionIdGenerator: undefined, // Stateless: no session management
         });
 
+        res.on('close', () => {
+          transport.close();
+          server.close();
+        });
+
         await server.connect(transport);
         await transport.handleRequest(req, res, req.body);
       } catch (error) {