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-engine-dedup.md

@@ -130,3 +130,11 @@ These are small blocks but appear in both send and recv tasks. Extract as inline
 - Audio I/O trait abstraction (Oboe vs CPAL) — different project, different risk profile
 - Moving Android-specific diagnostics (first-join, PCM recorder) into a feature flag
 - Splitting engine.rs into multiple files
+
+## Implementation Status (2026-04-13)
+
+All phases implemented:
+- build_call_config(): shared CallConfig construction — DONE
+- codec_to_profile(): shared CodecId → QualityProfile mapping — DONE
+- run_signal_task(): shared signal handler — DONE
+- Net reduction: ~39 lines, 6 duplicated blocks → single-line calls