separate personality from system instructions
phi.md is now pure identity/voice — removed capabilities list (redundant
with tool docstrings), response format (moved to Response model fields),
tool discipline (folded into engagement section), and platform constraints
(handled by code). operational guardrails live in agent.py as a separate
constant appended to the system prompt.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>