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>

src/services/session-share-events.ts

@@ -48,6 +48,9 @@ type EventDelegate = {
     orderBy: { createdAt: 'desc' };
     select: { createdAt: true };
   }) => Promise<{ createdAt: Date } | null>;
+  deleteMany: (args: {
+    where: { createdAt: { lt: Date } };
+  }) => Promise<unknown>;
 };
 
 type SessionDelegate = {
@@ -168,5 +171,13 @@ export function createShareAndEventHandlers<TEventType extends string>(
       });
       return event?.createdAt;
     },
+
+    /** Delete events older than the given number of hours (default: 24h) */
+    async cleanupOldEvents(maxAgeHours = 24) {
+      const cutoff = new Date(Date.now() - maxAgeHours * 60 * 60 * 1000);
+      return eventModel.deleteMany({
+        where: { createdAt: { lt: cutoff } },
+      });
+    },
   };
 }