docs: update all PRDs and PROGRESS to current state (2026-04-13)

Updated 6 PRDs with implementation status:
- PRD-adaptive-quality: P2P quality done, bandwidth probing remains
- PRD-protocol-analyzer: all 5 phases documented
- PRD-relay-concurrency: DashMap + clone-before-send done
- PRD-p2p-direct: P2P adaptive quality update
- PRD-engine-dedup: all phases done
- PROGRESS.md: test count 372+, 3 new change sections

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

docs/PRD-relay-concurrency.md

@@ -304,3 +304,11 @@ Option: Move quality observation to a background task:
 - Phase 2: 0.5 day (federation clone-and-release)
 - Phase 3: 0.5 day (optional, quality tracking with atomics)
 - Total: 1.5–2 days
+
+## Implementation Status (2026-04-13)
+
+Phase 1 (DashMap): DONE — global Mutex → DashMap<String, Room> with 64 shards
+Phase 2 (Federation clone-before-send): DONE — forward_to_peers, broadcast_signal, send_signal_to_peer
+Phase 3 (Quality atomics): NOT DONE — optional optimization
+
+See also: docs/REFACTOR-relay-concurrency.md for the full post-refactor analysis.