refactor: slim AGENTS.md to identity-only content
Remove operational sections (Adaptive Depth, Skills, Speaker Intelligence,
Routines, Support, Onboarding) that are now loaded via facets/skills rather
than baked into the static agent prompt. Replace with concise Partnership
and Resilience sections.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>