feat: Stage 1 — TimelineReconstructor for multi-agent diagnose pipeline (issue #29)
- Add app/services/diagnose/timeline.py: pure-Python TimelineReconstructor
- Sorts entries by timestamp_iso (None entries appended at end)
- Sliding-window clustering anchored to first entry in each cluster
- Computes cluster_id (sha1[:12]), severity (highest wins), burst flag,
gap_before_seconds, representative_text (highest rank, longest text tiebreak)
- Builds TimelineResult with dominant_sources sorted by entry count descending
- Update pipeline.py stub to import TimelineReconstructor (Task 6 wiring prep)
- Add tests/test_diagnose_timeline.py: 15 tests covering all 13 required cases
plus null-timestamp edge case variant; all 318 tests passing
Closes: #29
pyr0ball
7cff98b1c3