feat: separate live early-warning + combined score on the regime tab

The event study showed the breadth-divergence signal genuinely leads (warned
before 7/11 drawdowns, ~6 weeks median, where the coincident baseline almost
never did). Surface it live to observe before deciding how to embed it — kept
separate from the index, not folded into its weights.

- regime_monitor daily job now computes breadth-divergence live and attaches a
  separate early_warning score plus a combined blend (weighted mean, default
  0.6/0.4, configurable via combined_weights) to each snapshot, including the
  backfill so the 7/30-day trends populate immediately. Stored in breakdown_json
  — no schema change. Best-effort: a breadth failure can't break the index.
- get_regime_monitor returns the index, early_warning, and combined scores each
  with 7/30-day deltas.
- Regime tab shows three gauges (generalized ScoreGauge): coincident index,
  early warning, and a compact combined blend. Stale snapshots render "—".

Note: the daily regime job now also does a universe-wide breadth scan.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

tests/unit/test_regime_monitor.py

@@ -6,6 +6,7 @@ from datetime import date, timedelta
 
 from app.services.regime_monitor_service import (
     DEFAULT_CONFIG,
+    _attach_early_warning,
     band_for,
     compute_regime_score,
     f2_credit_spreads,
@@ -35,6 +36,23 @@ def test_band_for():
     assert band_for(90) == "breaking"
 
 
+def test_attach_early_warning_blends():
+    result = {"total_score": 80.0}
+    _attach_early_warning(result, 40.0, {"coincident": 0.6, "early_warning": 0.4})
+    assert result["early_warning"]["score"] == 40.0
+    assert result["early_warning"]["band"] == "watch"
+    # combined = (80*0.6 + 40*0.4) / 1.0 = 64
+    assert result["combined"]["score"] == 64.0
+    assert result["combined"]["band"] == "elevated"
+
+
+def test_attach_early_warning_none_falls_back_to_index():
+    result = {"total_score": 80.0}
+    _attach_early_warning(result, None, {"coincident": 0.6, "early_warning": 0.4})
+    assert result["early_warning"]["score"] is None
+    assert result["combined"]["score"] == 80.0  # no early warning -> just the index
+
+
 # ---------------------------------------------------------------------------
 # Price sub-scores
 # ---------------------------------------------------------------------------