Restructured AGENTS.md from a 588-line catch-all into a lean reference of essential rules by offloading deep guidance into five new/expanded doc files: agents.md, architecture.md, dashboard-guide.md, settings-reference.md, and testing.md. Also restored a missing FN-5345 lifecycle invariant in self-h
Fusion-Task-Id: FN-5339
Fusion-Task-Lineage: e1a2dc4f-ae50-46f4-acd3-8f2c3673feb4
