feat: personal bot for slack

### 使用场景 / Use case

If implemented, Cindy works as a bot, then it can help team members.
So far, the official Cindy app can only help myself.

### 当前问题 / Current limitation

The official Cindy app can only help myself. In a Slack channel, I will need Cindy to respond to both my and my teammates' messages.

### 期望方案 / Proposed solution

I hope Cindy.app can support a person bot for Slack.

### 已考虑的替代方案 / Alternatives considered

_No response_

The issue names no files, tests, or entry points. Start by locating the existing Slack integration and the official Cindy app flow, then determine how a person bot would be configured and invoked. Done means Cindy can respond to messages from both the reporter and teammates in a Slack channel.

Written by the indexing model from the issue text.