feat: add WeChat QR code login and AGP WebSocket channel plugin

- Auth module: WeChat OAuth2 scan-to-login flow with terminal QR code
- Token persistence to ~/.openclaw/wechat-access-auth.json (chmod 600)
- Token resolution: config > saved state > interactive login
- Invite code verification (configurable bypass)
- Production/test environment support
- AGP WebSocket client with heartbeat, reconnect, wake detection
- Message handler: Agent dispatch with streaming text and tool calls
- Random device GUID generation (persisted, no real machine ID)

http/message-context.ts

@@ -0,0 +1,4 @@
+// 已迁移至 common/message-context.ts
+// 此文件保留以兼容现有 http 模块内部引用
+export type { MessageContext } from "../common/message-context.js";
+export { buildMessageContext, WECHAT_CHANNEL_LABELS } from "../common/message-context.js";