feat(channel): Improve and Enrich Channel Implementation in Agent Service

**Background**

The basic channel functionality has been established in v2.0.6 (#1997), with support for Feishu and Discord channels. However, further improvements are needed, including:

- Add new channel support, initially planned for WeCom (企业微信) and DingTalk
- Improve existing implementations:
- `DiscordChannel`: add `list_tools` support to expose corresponding tools
- Feishu, DingTalk and other IM channels: support adding a channel by scanning a QR code instead of manually entering the app ID and secret key
- Integrate channel with scheduled tasks, enabling scheduled triggers to wake up an agent and complete corresponding tasks in the target channel

**Tasks**

- Add WeCom channel support
- Add DingTalk channel support
- `DiscordChannel`: implement `list_tools`
- QR code-based channel binding for IM channels (Feishu, DingTalk, etc.)
- Integrate channel with scheduled task mechanism