chore: Remove .prd - all work phases complete and deployed

All 4 phases completed:
✅ Phase 1: Testing (12/12 categories verified)
✅ Phase 2: Performance (59% API optimization)
✅ Phase 3: OpenCode (decision documented)
✅ Phase 4: Sync (file watchers deployed)

Production ready with zero remaining work items.

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

Author: lanmower