Northstar Architecture Refocus

Thin explicit entrypoint for the canonical architecture-refocus route.

1. Load references/router.md from the main northstar skill.
2. Select Architecture refocus and load references/modes/architecture-refocus.md.
3. Follow that mode's bounded, evidence-led candidate procedure.
4. Treat the text after /northstar-architecture-refocus as the codebase seam or architecture question.

Remain plan-only. Do not edit production code, start workers, create worktrees, authorize execution, or merge anything.