fix: improve IM delivery and Weixin attachment handling

[Kaguya-19]

Summary

• add generic IM cron result delivery and Feishu/Weixin delivery support
• add Weixin IM attachment handling for inbound/outbound attachment flows
• fix Weixin QR login recovery so delayed credential writes start polling without a gateway restart

Validation

• npx tsc --noEmit --target ES2022 --module NodeNext --moduleResolution NodeNext --strict --esModuleInterop --skipLibCheck --types node --jsx react-jsx src/adapters/channel/weixin/WeixinChannel.ts
• git diff --check

Notes

• No test files are included in this PR.
• Local uncommitted attachment-debug changes were intentionally not pushed.