Pitch

We have profile support in `config.toml` (`[profiles.work]`, `[profiles.personal]`) plus the `--profile` CLI flag. What's missing is the in-session switch:

```
/profile — show current + list available
/profile work — switch to [profiles.work] without restart
/profile personal — switch to [profiles.personal]
```

Switching reloads the config layer (model, base_url, hooks, MCP servers, permissions, etc.) and rebuilds the engine in place — same plumbing as `/logout` already does for credentials.

Acceptance

• `/profile` (no args) shows current + lists available profiles.
• `/profile ` switches without restart, refreshes engine, status toast.
• `/profile ` errors with a list of valid names.
• Documented in /help.