Non-interactive mode to support slash command invocation

### Feature Description

Non-interactive mode should support slash command when invoked, for example. 

```
cmd -p "/review this branch"
```

### Use Case

Any non-interactive usage should support all features of the CLI.

### Additional Context

Requested by user: https://discord.com/channels/1255220079029653626/1505264904586793161

### How important is this to you?

Fundamental functionality. 