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>

src/message-transport.ts

@@ -82,7 +82,7 @@ export class PostMessageTransport implements Transport {
       }
       const parsed = JSONRPCMessageSchema.safeParse(event.data);
       if (parsed.success) {
-        console.info("[host] Parsed message", parsed.data);
+        console.debug("Parsed message", parsed.data);
         this.onmessage?.(parsed.data);
       } else {
         console.error("Failed to parse message", parsed.error.message, event);
@@ -115,7 +115,7 @@ export class PostMessageTransport implements Transport {
    * @param options - Optional send options (currently unused)
    */
   async send(message: JSONRPCMessage, options?: TransportSendOptions) {
-    console.info("[host] Sending message", message);
+    console.debug("Sending message", message);
     this.eventTarget.postMessage(message, "*");
   }