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/hooks/useAdmin.ts

@@ -114,6 +114,32 @@ export function useUpdateRecommendationSettings() {
   });
 }
 
+export function useActivationSettings() {
+  return useQuery({
+    queryKey: ['admin', 'activation-settings'],
+    queryFn: () => adminApi.getActivationSettings(),
+  });
+}
+
+export function useUpdateActivationSettings() {
+  const qc = useQueryClient();
+  const { addToast } = useToast();
+
+  return useMutation({
+    mutationFn: (payload: Record<string, number>) =>
+      adminApi.updateActivationSettings(payload),
+    onSuccess: () => {
+      qc.invalidateQueries({ queryKey: ['admin', 'activation-settings'] });
+      qc.invalidateQueries({ queryKey: ['activation'] });
+      qc.invalidateQueries({ queryKey: ['performance'] });
+      addToast('success', 'Activation thresholds updated');
+    },
+    onError: (error: Error) => {
+      addToast('error', error.message || 'Failed to update activation thresholds');
+    },
+  });
+}
+
 export function useTickerUniverseSetting() {
   return useQuery({
     queryKey: ['admin', 'ticker-universe'],