Northstar Cleanup

Thin explicit entrypoint for the canonical docs-cleanup route.

1. Load references/router.md from the main northstar skill.
2. Select Docs cleanup and load references/modes/cleanup-docs.md.
3. Follow that mode's inventory, classification, bounded-repair, and triage disposition procedure. Report proposed closed-generation compaction; remain read-only until repair is already allowed.
4. Treat the text after /northstar-cleanup as the docs tree or cleanup question to inspect.

Remain read-only unless the operator explicitly authorizes bounded docs repair. Do not blindly delete files, start workers, create worktrees, authorize execution, or merge anything.