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/base/package.json

@@ -3,10 +3,19 @@
   "version": "0.1.0",
   "description": "Base channel infrastructure for Qwen Code",
   "type": "module",
-  "main": "src/index.ts",
-  "types": "src/index.ts",
+  "main": "dist/index.js",
+  "types": "dist/index.d.ts",
   "exports": {
-    ".": "./src/index.ts"
+    ".": {
+      "types": "./dist/index.d.ts",
+      "default": "./dist/index.js"
+    }
+  },
+  "files": [
+    "dist"
+  ],
+  "scripts": {
+    "build": "tsc --build"
   },
   "dependencies": {
     "@agentclientprotocol/sdk": "^0.14.1"