Add basic-host and basic-server-react examples

Introduce new example implementations to replace simple-host and
simple-server:

- basic-host: Reference host implementation with double-iframe sandbox
  pattern for secure UI isolation (outer iframe validates and relays
  messages, inner iframe renders untrusted tool UI via srcdoc)

- basic-server-react: MCP server example demonstrating tool registration
  with linked UI resources and React UI using the useApp() hook

Build infrastructure updates:
- Add build:all script and simplify CI/pre-commit to use it
- Add examples:dev for watch-mode development workflow

Also change PostMessageTransport logging from info to debug level.

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

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

examples/basic-server-react/package.json

@@ -0,0 +1,34 @@
+{
+  "name": "basic-server-react",
+  "version": "1.0.0",
+  "private": true,
+  "type": "module",
+  "scripts": {
+    "build": "INPUT=mcp-app.html vite build",
+    "watch": "INPUT=mcp-app.html vite build --watch",
+    "serve": "bun server.ts",
+    "start": "NODE_ENV=development npm run build && npm run serve",
+    "dev": "NODE_ENV=development concurrently 'npm run watch' 'npm run serve'"
+  },
+  "dependencies": {
+    "@modelcontextprotocol/ext-apps": "../..",
+    "@modelcontextprotocol/sdk": "^1.22.0",
+    "react": "^19.2.0",
+    "react-dom": "^19.2.0",
+    "zod": "^3.25.0"
+  },
+  "devDependencies": {
+    "@types/cors": "^2.8.19",
+    "@types/express": "^5.0.0",
+    "@types/node": "^22.0.0",
+    "@types/react": "^19.2.2",
+    "@types/react-dom": "^19.2.2",
+    "@vitejs/plugin-react": "^4.3.4",
+    "concurrently": "^9.2.1",
+    "cors": "^2.8.5",
+    "express": "^5.1.0",
+    "typescript": "^5.9.3",
+    "vite": "^6.0.0",
+    "vite-plugin-singlefile": "^2.3.0"
+  }
+}