feat: impersonation system, semi-finalist detail page, tRPC resilience

- Add super-admin impersonation: "Login As" from user list, red banner
  with "Return to Admin", audit logged start/end, nested impersonation
  blocked, onboarding gate skipped during impersonation
- Fix semi-finalist stats: check latest terminal state (not any PASSED),
  use passwordHash OR status=ACTIVE for activation check
- Add /admin/semi-finalists detail page with search, category/status filters
- Add account_reminder_days setting to notifications tab
- Add tRPC resilience: retry on 503/HTML responses, custom fetch detects
  nginx error pages, exponential backoff (2s/4s/8s)
- Reduce dashboard polling intervals (60s stats, 30s activity, 120s semi)

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

src/app/(admin)/admin/dashboard-content.tsx

@@ -116,20 +116,21 @@ function getContextualActions(
 export function DashboardContent({ editionId, sessionName }: DashboardContentProps) {
   const { data, isLoading, error } = trpc.dashboard.getStats.useQuery(
     { editionId },
-    { enabled: !!editionId, retry: 1, refetchInterval: 30_000 }
+    { enabled: !!editionId, refetchInterval: 60_000 }
   )
   const { data: recentEvals } = trpc.dashboard.getRecentEvaluations.useQuery(
     { editionId, limit: 8 },
-    { enabled: !!editionId, refetchInterval: 30_000 }
+    { enabled: !!editionId, refetchInterval: 60_000 }
   )
   const { data: liveActivity } = trpc.dashboard.getRecentActivity.useQuery(
     { limit: 8 },
-    { enabled: !!editionId, refetchInterval: 5_000 }
+    { enabled: !!editionId, refetchInterval: 30_000 }
   )
   const { data: semiFinalistStats } = trpc.dashboard.getSemiFinalistStats.useQuery(
     { editionId },
-    { enabled: !!editionId, refetchInterval: 60_000 }
+    { enabled: !!editionId, refetchInterval: 120_000 }
   )
+  const { data: featureFlags } = trpc.settings.getFeatureFlags.useQuery()
 
   if (isLoading) {
     return <DashboardSkeleton />
@@ -283,6 +284,7 @@ export function DashboardContent({ editionId, sessionName }: DashboardContentPro
                 byAward={semiFinalistStats.byAward}
                 unactivatedProjects={semiFinalistStats.unactivatedProjects}
                 editionId={editionId}
+                reminderThresholdDays={featureFlags?.accountReminderDays}
               />
             </AnimatedCard>
           )}