[Feature Request] Implement hot-reloading for slash commands based on file mtime

Question

**Bug Description**
Slash commands do not reload immediately on change. You have to quit `claud` and go back in, which is rather annoying. Doing a simple `stat` and getting an `mtime` is nice and fast. Every time a slash command is run, it should check to see if the timestamp changed since the previous load and reload it if necessary.

**Environment Info**
- Platform: linux
- Terminal: vte-based
- Version: 2.0.25
- Feedback ID: 96e42269-455d-4663-ab50-a7a6384ef2a3

**Errors**
```json
[]
```