Refactor incident_correlator.py to a decision/commit split (preview_correlation
/ apply_correlation) so the rules engine and LLM can both produce decisions before
anything is written to Firestore.
Add llm_correlator.py: cheap Gemini Flash first-pass + Gemini Pro tiebreaker.
Wire _correlate_with_consensus in upload.py — rules-only fallback when key is
absent or call is thin; agreed/tiebreak consensus written to corr_debug.