feat: 注册内建 weixin channel 插件

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

src/plugins/bundled/weixin.ts

@@ -0,0 +1,21 @@
+import { registerBuiltinPlugin } from '../builtinPlugins.js'
+import { buildCliLaunch } from '../../utils/cliLaunch.js'
+
+export function registerWeixinBuiltinPlugin(): void {
+  const launch = buildCliLaunch(['weixin', 'serve'])
+
+  registerBuiltinPlugin({
+    name: 'weixin',
+    description:
+      'WeChat channel integration. Enables inbound WeChat messages via channels and provides reply/send_typing MCP tools. Configure with `ccb weixin login` and enable for a session with `--channels plugin:weixin@builtin`.',
+    version: MACRO.VERSION,
+    defaultEnabled: true,
+    mcpServers: {
+      weixin: {
+        type: 'stdio',
+        command: launch.execPath,
+        args: launch.args,
+      },
+    },
+  })
+}