feat(debug-server): add interactive debug server example (#321)

* feat(examples): add debug-server example

A comprehensive debug/development server for testing MCP Apps SDK features:
- Vanilla TypeScript UI with collapsible panels
- Message visualization (sent, received, errors)
- Server tool calling interface
- Multiple tool endpoints for testing

* refactor(debug-server): convert to React

- Replace vanilla TypeScript with React components
- Add comprehensive Host Styles panel showing all CSS variables grouped by category
- Use React hooks (useApp, useHostStyles, useAutoResize)
- Cleaner state management with useReducer for event log
- Collapsible sections for better organization
- CSS modules for scoped styling

* fix(debug-server): correct server name in main.ts

* Revert "refactor(debug-server): convert to React"

This reverts commit 5d22d2daa9a98ba412892447202ef10fbdb62f5b.

* fix(debug-server): update default values for multipleBlocks and includeMeta

* fix(debug-server): correct serve script and server name

- serve script now runs main.ts instead of server.ts
- Updated server name to 'Debug Server'
- Fixed npx command in comment

* fix: increase maxHeight to 6000px and add tools capability to debug app

- basic-host: Increase maxHeight from 600 to 6000px
- debug-server: Add tools capability to enable oncalltool/onlisttools handlers

* fix(debug-server): use consistent callback names for event tracking

Event types now match callback names (ontoolinput, ontoolresult, etc.)
so the Callback Status panel shows correct counts and payloads.

* feat(debug-server): add Update (Image) button for model context

* feat(debug-server): add expandable event log entries

- Click on any event log row to expand/collapse
- Arrow indicator rotates when expanded
- Full JSON payload shown indented in pre block
- Max height with scroll for large payloads

* style(debug-server): format long line in fullPayload function

* test(debug-server): add to E2E tests and screenshot specs

* chore: regenerate package-lock.json for cross-platform compatibility

* update dep

examples/debug-server/README.md

@@ -0,0 +1,55 @@
+# Debug Server
+
+A comprehensive testing/debugging tool for the MCP Apps SDK that exercises every capability, callback, and result format combination.
+
+## Tools
+
+### debug-tool
+
+Configurable tool for testing all result variations:
+
+| Parameter                  | Type                                                                                | Default  | Description                                 |
+| -------------------------- | ----------------------------------------------------------------------------------- | -------- | ------------------------------------------- |
+| `contentType`              | `"text"` \| `"image"` \| `"audio"` \| `"resource"` \| `"resourceLink"` \| `"mixed"` | `"text"` | Content block type to return                |
+| `multipleBlocks`           | boolean                                                                             | `false`  | Return 3 content blocks                     |
+| `includeStructuredContent` | boolean                                                                             | `true`   | Include structuredContent in result         |
+| `includeMeta`              | boolean                                                                             | `false`  | Include \_meta in result                    |
+| `largeInput`               | string                                                                              | -        | Large text input (tests tool-input-partial) |
+| `simulateError`            | boolean                                                                             | `false`  | Return isError: true                        |
+| `delayMs`                  | number                                                                              | -        | Delay before response (ms)                  |
+
+### debug-refresh
+
+App-only tool (hidden from model) for polling server state. Returns current timestamp and call counter.
+
+## App UI
+
+The debug app provides a dashboard with:
+
+- **Event Log**: Real-time log of all SDK events with filtering
+- **Host Info**: Context, capabilities, container dimensions, styles
+- **Callback Status**: Table of all callbacks with call counts
+- **Actions**: Buttons to test every SDK method:
+  - Send messages (text/image)
+  - Logging (debug/info/warning/error)
+  - Model context updates
+  - Display mode requests
+  - Link opening
+  - Resize controls
+  - Server tool calls
+  - File operations
+
+## Usage
+
+```bash
+# Build
+npm run --workspace examples/debug-server build
+
+# Run standalone
+npm run --workspace examples/debug-server serve
+
+# Run with all examples
+npm start
+```
+
+Then open `http://localhost:8080/basic-host/` and select "Debug MCP App Server" from the dropdown.