perf: optimize DB queries, SSE polling, and client rendering

- Fix resolveCollaborator N+1: replace full User table scan with findFirst
- Fix getAllUsersWithStats N+1: use groupBy instead of per-user count queries
- Cache getTeamMemberIdsForAdminTeams and isAdminOfUser with React.cache
- Increase SSE poll interval from 1s to 2s across all 5 subscribe routes
- Add cleanupOldEvents method to session-share-events for event table TTL
- Add React.memo to all card components (Swot, Motivator, Weather, WeeklyCheckIn, YearReview)
- Fix WeatherCard useEffect+setState lint error with idiomatic prop sync pattern
- Add optimizePackageImports for DnD libs and poweredByHeader:false in next.config
- Add inline theme script in layout.tsx to prevent dark mode FOUC
- Remove unused Next.js template SVGs from public/

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

next.config.ts

@@ -2,6 +2,15 @@ import type { NextConfig } from "next";
 
 const nextConfig: NextConfig = {
   output: "standalone",
+  poweredByHeader: false,
+  experimental: {
+    optimizePackageImports: [
+      "@dnd-kit/core",
+      "@dnd-kit/sortable",
+      "@dnd-kit/utilities",
+      "@hello-pangea/dnd",
+    ],
+  },
 };
 
 export default nextConfig;