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/README.md

@@ -0,0 +1,27 @@
+# Example: Basic Server (React)
+
+An MCP App example with a React UI.
+
+## Overview
+
+- Tool registration with a linked UI resource
+- React UI using the [`useApp()`](https://modelcontextprotocol.github.io/ext-apps/api/functions/_modelcontextprotocol_ext-apps_react.useApp.html) hook
+- App communication APIs: [`callServerTool`](https://modelcontextprotocol.github.io/ext-apps/api/classes/app.App.html#callservertool), [`sendMessage`](https://modelcontextprotocol.github.io/ext-apps/api/classes/app.App.html#sendmessage), [`sendLog`](https://modelcontextprotocol.github.io/ext-apps/api/classes/app.App.html#sendlog), [`sendOpenLink`](https://modelcontextprotocol.github.io/ext-apps/api/classes/app.App.html#sendopenlink)
+
+## Key Files
+
+- [`server.ts`](server.ts) - MCP server with tool and resource registration
+- [`mcp-app.html`](mcp-app.html) / [`src/mcp-app.tsx`](src/mcp-app.tsx) - React UI using `useApp()` hook
+
+## Getting Started
+
+```bash
+npm install
+npm run dev
+```
+
+## How It Works
+
+1. The server registers a `get-time` tool with metadata linking it to a UI HTML resource (`ui://get-time/mcp-app.html`).
+2. When the tool is invoked, the Host renders the UI from the resource.
+3. The UI uses the MCP App SDK API to communicate with the host and call server tools.