feat(channels): make plugin-example package publishable

- Update channel-base to use built dist/ output with proper exports
- Add README with quick start guide and usage instructions
- Add qwen-extension.json manifest for extension discovery
- Add start-server CLI for running the mock WebSocket server
- Update dependencies from local file: to npm version

This enables the plugin-example package to be published and installed
as a standalone extension for testing the channel plugin system.

Co-authored-by: Qwen-Coder <qwen-coder@alibabacloud.com>

packages/channels/plugin-example/src/start-server.ts

@@ -0,0 +1,36 @@
+#!/usr/bin/env node
+/* eslint-disable no-console */
+/**
+ * Start the mock WebSocket server for testing the plugin-example channel.
+ *
+ * Usage:
+ *   npx qwen-channel-plugin-example-server
+ *   # or
+ *   node node_modules/@qwen-code/channel-plugin-example/dist/start-server.js
+ *
+ * Environment variables:
+ *   HTTP_PORT  (default: 9200)
+ *   WS_PORT    (default: 9201)
+ */
+import { createMockServer } from './mock-server.js';
+
+const httpPort = parseInt(process.env['HTTP_PORT'] || '9200', 10);
+const wsPort = parseInt(process.env['WS_PORT'] || '9201', 10);
+
+const server = await createMockServer({ httpPort, wsPort });
+
+console.log(`Mock server running:`);
+console.log(`  HTTP: http://localhost:${server.httpPort}`);
+console.log(`  WS:   ws://localhost:${server.wsPort}`);
+console.log();
+console.log(`Send a test message:`);
+console.log(`  curl -sX POST http://localhost:${server.httpPort}/message \\`);
+console.log(`    -H 'Content-Type: application/json' \\`);
+console.log(
+  `    -d '{"senderId":"user1","senderName":"Tester","text":"Hello"}'`,
+);
+
+process.on('SIGINT', async () => {
+  await server.close();
+  process.exit(0);
+});