fix(app): auto-register tools capability in registerTool

When registerTool is called before connect() on an App created without
explicit tools capability, setRequestHandler's capability assertion
would throw, breaking app initialization at module load.

Auto-register { tools: { listChanged: true } } on first registerTool
call (pre-connect only), mirroring McpServer.registerTool behavior.

Fixes pdf-annotations e2e failures where the PDF canvas never rendered
because registerTool threw at module scope.

Author: ochafik

src/app.ts

@@ -352,6 +352,15 @@ export class App extends Protocol<AppRequest, AppNotification, AppResult> {
 
     this._registeredTools[name] = registeredTool;
 
+    // Auto-register tools capability so setRequestHandler's capability check
+    // passes. Mirrors McpServer.registerTool behavior — callers shouldn't need
+    // to declare { tools: {} } in the constructor just to use registerTool.
+    // Only do this pre-connect; post-connect the capability was already
+    // advertised (or wasn't) and can't change.
+    if (!this._capabilities.tools && !this.transport) {
+      this.registerCapabilities({ tools: { listChanged: true } });
+    }
+
     this.ensureToolHandlersInitialized();
     return registeredTool;
   }