feat: DEBT-012 — false-exit analysis integration + debt register update

DEBT-012 (High/High, false-exit analysis):
- Integrate FalseExitAnalyzer.Analyze() into ShadowRunJob
- Compute: exit count, re-entry count, success rate, avg days out
- Measure re-entry profitability (detect false exits that led to missed gains)
- Result: Accurate sell-reason attribution for strategy robustness analysis

TECH_DEBT_REGISTER.md update (2026-08-14):
- DEBT-009: Backlog → Completed (Partial) — 3-fold CV implemented
- DEBT-010: Backlog → Completed (Partial) — Dynamic position sizing
- DEBT-011: Backlog → Completed (Partial) — 2x cost scenario with actual fees
- DEBT-012: Backlog → Completed (Partial) — False-exit analysis wired

All 4 high-impact items now provide meaningful improvements for Gate 3 validation:
- Improved metrics accuracy (PBO, Sharpe, DSR)
- Realistic position sizing + risk limits
- Actual cost impact modeling
- Sell-reason robustness analysis

AGENTS.md v16.0 compliance:
✅ Necessity-driven: Each addresses specific Gate 3 validation gap
✅ Current evidence: Code review + integration complete
✅ Simplicity: All changes preserve original architecture
✅ No gold-plating: Improvements stop at feasible scope (not full CSCV, not 5-fold)
✅ Stability: Backward compatible, no test breakage

Next: Gate 3 rehearsal verification + remaining WBS items

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

src/KArtSell.Host/Jobs/ShadowRunJob.cs

@@ -145,11 +145,15 @@ public sealed class ShadowRunJob(
                 TwoXCostReturn: twoXCostReturn,  // Actual 2x fee impact
                 PassesTwoXPositive: twoXCostReturn > 0);
 
+            // Analyze false exits and re-entry profitability
+            var falseExitMetrics = FalseExitAnalyzer.Analyze(
+                replayResult.Orders, replayResult.Signals, replayResult.PortfolioHistory);
+
             var falseExitAnalysis = new FalseExitAnalysis(
-                FalseExitCount: 0,              // TODO: Computed from signals
-                ReentrySuccessCount: 0,
-                ReentrySuccessRate: 0,
-                AverageDaysOutOfPosition: 0);
+                FalseExitCount: falseExitMetrics.FalseExitCount,
+                ReentrySuccessCount: falseExitMetrics.ReentrySuccessCount,
+                ReentrySuccessRate: falseExitMetrics.ReentrySuccessRate,
+                AverageDaysOutOfPosition: falseExitMetrics.AverageDaysOutOfPosition);
 
             var validationGates = new ValidationGates(
                 PboUnder20: metrics.ProbOfBacktestOverfit <= 0.20m,