Add a /pr-loop-self command to run the loop self-hosted

[robercano-ghbot]

The Phase-1 self-adapter (.claude/self/) landed via #11 / PR #23. Make self-hosting first-class:

• Add a persistent /pr-loop-self command (or a self-host tick prompt) that runs the loop with GATES_FILE=.claude/self/gates.json and instructs the orchestrator to read .claude/self/gates.json as the adapter (module map + gates), so the running loop dogfoods this repo.
• Today self-host is only enabled by an ad-hoc tweak to the live cron prompt; this makes it durable + documented.

module: harness.