feat: implement ui/notifications/tool-cancelled + add missing App.onteardown (#120)

* feat: implement ui/notifications/tool-cancelled throughout SDK

Wire the tool-cancelled notification that hosts MUST send when tool
execution is cancelled (user action, timeout, classifier intervention, etc.):

- Add McpUiToolCancelledNotification type in spec.types.ts
- Generate Zod schema via ts-to-zod
- Add AppBridge.sendToolCancelled() method for hosts
- Add App.ontoolcancelled setter for guest UIs
- Export type and schema from types.ts
- Add tests for notification with/without reason

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

* feat: add App.onteardown handler for graceful shutdown

Wire the guest UI side of ui/resource-teardown request:

- Add onteardown setter in App class for guest UIs to handle teardown
- Allow ui/resource-teardown in assertRequestHandlerCapability
- Import McpUiResourceTeardownRequest/Result types
- Add tests for sync and async cleanup handlers

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

* feat(example): wire tool-cancelled and teardown in basic-host

Update basic-host example to properly use the new notifications:

- Send sendToolCancelled when tool call promise rejects
- Send sendResourceTeardown when React component unmounts
- Store appBridge ref for cleanup access

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

* fix(example): implement graceful teardown per spec recommendation

Address review feedback: the host now waits for guest's teardown
response before unmounting, following the spec: "Host SHOULD wait
for a response before tearing down the resource (to prevent data loss)."

Changes:
- Add close button to tool call panels
- Two-phase unmount: isDestroying state dims panel and disables events
- sendResourceTeardown() completes before component removal
- Non-app tool results close immediately

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

* feat(examples): add onteardown handlers to demo apps

Demonstrate graceful shutdown with simulated 500ms cleanup work.

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

---------

Co-authored-by: Claude <noreply@anthropic.com>

src/app-bridge.test.ts

@@ -140,6 +140,36 @@ describe("App <-> AppBridge integration", () => {
       });
     });
 
+    it("sendToolCancelled triggers app.ontoolcancelled", async () => {
+      const receivedCancellations: unknown[] = [];
+      app.ontoolcancelled = (params) => {
+        receivedCancellations.push(params);
+      };
+
+      await app.connect(appTransport);
+      await bridge.sendToolCancelled({
+        reason: "User cancelled the operation",
+      });
+
+      expect(receivedCancellations).toHaveLength(1);
+      expect(receivedCancellations[0]).toEqual({
+        reason: "User cancelled the operation",
+      });
+    });
+
+    it("sendToolCancelled works without reason", async () => {
+      const receivedCancellations: unknown[] = [];
+      app.ontoolcancelled = (params) => {
+        receivedCancellations.push(params);
+      };
+
+      await app.connect(appTransport);
+      await bridge.sendToolCancelled({});
+
+      expect(receivedCancellations).toHaveLength(1);
+      expect(receivedCancellations[0]).toEqual({});
+    });
+
     it("setHostContext triggers app.onhostcontextchanged", async () => {
       const receivedContexts: unknown[] = [];
       app.onhostcontextchanged = (params) => {
@@ -173,6 +203,34 @@ describe("App <-> AppBridge integration", () => {
         { theme: "light" },
       ]);
     });
+
+    it("sendResourceTeardown triggers app.onteardown", async () => {
+      let teardownCalled = false;
+      app.onteardown = async () => {
+        teardownCalled = true;
+        return {};
+      };
+
+      await app.connect(appTransport);
+      await bridge.sendResourceTeardown({});
+
+      expect(teardownCalled).toBe(true);
+    });
+
+    it("sendResourceTeardown waits for async cleanup", async () => {
+      const cleanupSteps: string[] = [];
+      app.onteardown = async () => {
+        cleanupSteps.push("start");
+        await new Promise((resolve) => setTimeout(resolve, 10));
+        cleanupSteps.push("done");
+        return {};
+      };
+
+      await app.connect(appTransport);
+      await bridge.sendResourceTeardown({});
+
+      expect(cleanupSteps).toEqual(["start", "done"]);
+    });
   });
 
   describe("App -> Host notifications", () => {