Rewrite coder agent as phased sub-agent orchestrator
Replace the flat "read, implement, test, commit" workflow in muse/coder.md
with a 5-phase orchestration pattern (prep → design → implement → audit →
commit). The coder agent now spawns focused sub-agents for each phase via
the Agent tool, with phase-specific tool restrictions and iteration logic
(implement ↔ audit loop with 3-cycle cap).
Development guidelines section updated to match current body reference
files, adding mypy, uv/make update, worktree development, test-apps/
test-only/coverage commands, and other previously missing content.