feat(core): IV-RV adaptive gate in validate_entry + tests

Quando iv_minus_rv_adaptive_enabled=True, la soglia diventa
max(P_q rolling, iv_minus_rv_min). Path legacy (statico) e
None-bypass restano invariati.

Aggiunge anche due model_validator a StrategyConfig per
fail-fast su config invalida (window_min_days < target_days,
percentile in (0,1)) — risponde alla code review T1.

Tests: pass/skip su rolling, warmup hard, floor binding,
backwards compat statico, None bypass.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/cerbero_bite/config/schema.py

@@ -407,6 +407,16 @@ class StrategyConfig(BaseModel):
         if self.entry.dvol_min >= self.entry.dvol_max:
             raise ValueError("dvol_min must be < dvol_max")
 
+        e = self.entry
+        if e.iv_minus_rv_window_min_days >= e.iv_minus_rv_window_target_days:
+            raise ValueError(
+                "iv_minus_rv_window_min_days must be < iv_minus_rv_window_target_days"
+            )
+        if not (Decimal("0") < e.iv_minus_rv_percentile < Decimal("1")):
+            raise ValueError(
+                "iv_minus_rv_percentile must be in (0, 1)"
+            )
+
         return self