Feature: tinyTikTok 业务层

**Is your feature request related to a problem? Please describe.**
复杂的处理，但不会在这里涉及并发，业务逻辑为主

**Describe the solution you'd like**
- [x] comment
- [x] favorite
- [x] feed
- [x] publish
- [x] user

**Describe alternatives you've considered**
A clear and concise description of any alternative solutions or features you've considered.

**Additional context**
Add any other context or screenshots about the feature request here.

No files, tests, or entry points are named. First map the project's business layer and define the scope and acceptance criteria for comment, favorite, feed, publish, and user features before implementation can begin.

Written by the indexing model from the issue text.