Add activation thresholds: qualified-signal defaults and views

Admin-configurable thresholds (min R:R, default 2.0; min confidence,
default 70%) defining what counts as an actionable signal:

- Admin Settings: new Activation Thresholds panel
  (GET/PUT /admin/settings/activation)
- GET /trades/activation exposes values to all users with access
- Signals/Setups: filters initialize from activation values
- Track Record: "Qualified signals only" toggle (default on) via
  min_rr/min_confidence params on /trades/performance; the
  confidence breakdown always covers the full population so the
  thresholds can be validated against outcomes
- Dashboard: "Qualified" metric and qualified-first Top Setups
- Outcome evaluator unchanged: every setup is still evaluated

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

frontend/src/lib/types.ts

@@ -152,6 +152,12 @@ export interface PerformanceStats {
   by_confidence: Record<string, OutcomeBucketStats>;
 }
 
+// Activation thresholds: what counts as an actionable signal
+export interface ActivationConfig {
+  min_rr: number;
+  min_confidence: number;
+}
+
 export interface TradeTarget {
   price: number;
   distance_from_entry: number;