feat: Data Management tab — purge endpoints for all major data stores

Backend — new DELETE /purge-all endpoints:
  - /api/logs/purge-all          → truncate system_logs (immediate, no 30d wait)
  - /api/reports/purge-all       → cycle_reports + ai_reports
  - /api/portfolio/purge-all     → portfolio + trade_entry_prices
  - /api/analytics/purge-all     → pattern_score_history, regime_clusters,
                                    pattern_embeddings, cycle_runs,
                                    macro_regime_history, geo_alert_history
  - /api/var/purge-all           → var_snapshots + pnl_snapshots
  - /api/pattern-lab/purge-all   → backtest_lab_runs

Frontend — Config.tsx: new 'Data Management' tab
  - PurgeButton component with inline double-confirm (click Purge → confirm)
  - Shows table names affected + row count deleted
  - 6 purge actions: Logs, AI Reports, Portfolio, Analytics, VaR, Pattern Lab

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

backend/routers/pattern_lab.py

@@ -164,6 +164,17 @@ def get_run(run_id: str):
     return _row_to_dict(_get_run(run_id))
 
 
+@router.delete("/purge-all")
+def purge_all_runs():
+    """Delete all Pattern Lab runs."""
+    conn = get_conn()
+    conn.execute("DELETE FROM backtest_lab_runs")
+    n = conn.total_changes
+    conn.commit()
+    conn.close()
+    return {"deleted": n}
+
+
 @router.delete("/runs/{run_id}")
 def delete_run(run_id: str):
     conn = get_conn()