correlation: rules decide, one cheap LLM call only when ambiguous; drop the consensus tiebreak (server-26#299)

The rules engine now commits every confident decision alone. _run_decision
marks a decision ambiguous (new_with_candidates, unfit_tg_candidate,
unverified_unit_link) and only then does upload._correlate make ONE
llm_correlator.decide call; a usable answer is committed, otherwise the rules
decision stands. Removed: _correlate_with_consensus, llm_correlator.tiebreak /
decisions_agree / tiebreak prompt, corr_smart_model, the correlation_smart
health tier, the LLM-orphan gate (_call_is_substanceless, effectively dead:
it could only fire on minor-severity untyped calls) and its sweep budget.
corr_consensus is now rules_only | llm | rules_fallback | rules_guard, with
corr_band naming why; admin debug and replay metrics read the new values.

Section fixes in the same pass:
- #115: no tiebreaker left to manufacture incidents; an LLM orphan of a
  rules "new" is honoured only for untyped, substanceless, routine/minor calls.
- #86: divergence veto bar moved to config (embedding_divergence_threshold);
  the band between it and the match bar is ambiguous, not a silent merge.
- #103: a unit link with no embedding is "unit_overlap_unverified" ->
  ambiguous, instead of skipping the veto and linking as verified.
- #189: unit-only and LLM links refused once an incident is open 90 min;
  unit links on incidents open >30 min are ambiguous; LLM links distance-
  guarded (incident_max_spread_km) and only to shown candidates.
- #190: severity steps down on an explicit stand-down phrase; new
  severity_peak keeps the monotonic max.
- #88: parse_llm_bool fails closed on "false"; scene closures honoured only
  on confident links or the incident the scene opened.
- #27: sweep budget is the scan window (wall clock), not 3 attempts.
- LLM prompt: "Reserve new" bullet no longer contradicts the #189 EXCEPT.
- updated_at never moves backward on a back-dated link.

Unmeasured: no live AI or replay (credits unfunded); band frequency, F1 and
thresholds are unverified. Must be re-scored on both answer keys in Replay
before merge.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

drb-c2-core/tests/test_ai_flag_gating.py

@@ -100,7 +100,7 @@ async def _run_ingest(global_correlation, system_ai_flags):
     )
     with g, sysdoc, \
          patch.object(upload, "fstore") as fs, \
-         patch.object(upload, "_correlate_with_consensus", AsyncMock(return_value=None)) as corr, \
+         patch.object(upload, "_correlate", AsyncMock(return_value=(None, {}))) as corr, \
          patch("app.internal.transcription.transcribe_call",
                AsyncMock(return_value=("units respond to main street", []))), \
          patch("app.internal.intelligence.extract_scenes", AsyncMock(return_value=[])) as scenes, \