Fix WeChat QR login cancellation and recovery

[webup]

What

• keep the WeChat QR login flow polling while the openclaw channels login command is still running
• keep Cancel enabled during QR scanning and clean up the active WeChat session with openclaw channels logout --channel wechat
• add an explicit timeout state with QR refresh recovery, and clean up the timed-out session before retry
• add focused Channels page tests for cancel, pending-login polling, and timeout recovery

Resolves #144.

Why

The WeChat QR setup flow could get stuck in a non-cancelable waiting state and gave users no recovery path after a stale QR session. The UI also needed to stay responsive while the underlying login command was still active.

How

• run the WeChat login command in the background while polling openclaw channels status
• invalidate stale attempts so late login failures cannot overwrite a newer connected or timedOut state
• call openclaw channels logout --channel wechat when canceling an active scan or refreshing after timeout
• extend the Channels tests to cover the new async state transitions

Verification

• npx vitest run src/modules/channels/__tests__/ChannelsPage.test.tsx
• npm run build
• live dev-browser verification on /channels: after 开始扫码登录, the modal stays in 等待扫码..., 取消 remains enabled, and cancel closes the dialog immediately

Screenshots

• Verified live with dev-browser on /channels in this CLI session; no GitHub-hosted screenshot asset was uploaded from the terminal session.