feat: IV gate — block ALERT trades before logging + configurable thresholds

- auto_cycle.py: pre-fetch IV snapshots at step 1.9; _apply_iv_gate() runs
  before log_trade_entries, removes ALERT-verdict trades (not just reports)
- options_technical_agent.py: _IVR_HIGH/_IVR_EXTREME/_SKEW_THRESH as
  module-level vars; straddle/strangle penalty -60 (vs -56 naked) at extreme IVR
  so Long Straddle at IVR ≥ 80% → ALERT; thresholds respected in rule engine
- database.py: seed 4 iv_gate config keys (iv_gate_enabled, iv_gate_ivr_high=60,
  iv_gate_ivr_extreme=80, iv_gate_skew_threshold=8) — editable from Config page
- Blocked trades logged as skipped_trades with [IV_GATE] detail + optimal strategy

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/services/database.py

@@ -499,6 +499,11 @@ def init_db():
     for _key, _val in [
         ("journal_retention_days", "90"),
         ("maturity_threshold_pct", "35"),
+        # IV Gate — blocks ALERT trades before they are logged
+        ("iv_gate_enabled", "true"),       # enable/disable the IV gate entirely
+        ("iv_gate_ivr_high", "60"),        # IVR above this = "high vol" (no naked long)
+        ("iv_gate_ivr_extreme", "80"),     # IVR above this = "extreme vol" (sell vol only)
+        ("iv_gate_skew_threshold", "8"),   # put skew above this = protect is expensive
     ]:
         existing = c.execute("SELECT value FROM config WHERE key=?", (_key,)).fetchone()
         if not existing: