perf(realtime+data): implement perf-data-optimization and perf-realtime-scale

## perf-data-optimization
- Add @@index([name]) on User model (migration)
- Add WEATHER_HISTORY_LIMIT=90 constant, apply take/orderBy on weather history queries
- Replace deep includes with explicit select on all 6 list service queries
- Add unstable_cache layer with revalidateTag on all list service functions
- Add cache-tags.ts helpers (sessionTag, sessionsListTag, userStatsTag)
- Invalidate sessionsListTag in all create/delete Server Actions

## perf-realtime-scale
- Create src/lib/broadcast.ts: generic createBroadcaster factory with shared polling
  (one interval per active session, starts on first subscriber, stops on last)
- Migrate all 6 SSE routes to use createBroadcaster — removes per-connection setInterval
- Add broadcastToXxx() calls in all Server Actions after mutations for immediate push
- Add SESSIONS_PAGE_SIZE=20, pagination on sessions page with loadMoreSessions action
- Add "Charger plus" button with loading state and "X sur Y" counter in WorkshopTabs

## Tests
- Add 19 unit tests for broadcast.ts (polling lifecycle, userId filtering,
  formatEvent, error resilience, session isolation)

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

src/services/moving-motivators.ts

@@ -1,3 +1,4 @@
+import { unstable_cache } from 'next/cache';
 import { prisma } from '@/services/database';
 import { resolveCollaborator, batchResolveCollaborators } from '@/services/auth';
 import { getTeamMemberIdsForAdminTeams } from '@/services/teams';
@@ -8,38 +9,50 @@ import {
   fetchTeamCollaboratorSessions,
   getSessionByIdGeneric,
 } from '@/services/session-queries';
+import { sessionsListTag } from '@/lib/cache-tags';
 import type { MotivatorType } from '@prisma/client';
 
-const motivatorInclude = {
+const motivatorListSelect = {
+  id: true,
+  title: true,
+  participant: true,
+  updatedAt: true,
+  userId: true,
   user: { select: { id: true, name: true, email: true } },
-  shares: { include: { user: { select: { id: true, name: true, email: true } } } },
+  shares: { select: { id: true, role: true, user: { select: { id: true, name: true, email: true } } } },
   _count: { select: { cards: true } },
-};
+} as const;
 
 // ============================================
 // Moving Motivators Session CRUD
 // ============================================
 
 export async function getMotivatorSessionsByUserId(userId: string) {
-  const sessions = await mergeSessionsByUserId(
-    (uid) =>
-      prisma.movingMotivatorsSession.findMany({
-        where: { userId: uid },
-        include: motivatorInclude,
-        orderBy: { updatedAt: 'desc' },
-      }),
-    (uid) =>
-      prisma.mMSessionShare.findMany({
-        where: { userId: uid },
-        include: { session: { include: motivatorInclude } },
-      }),
-    userId
-  );
-  const resolved = await batchResolveCollaborators(sessions.map((s) => s.participant));
-  return sessions.map((s) => ({
-    ...s,
-    resolvedParticipant: resolved.get(s.participant.trim()) ?? { raw: s.participant, matchedUser: null },
-  }));
+  return unstable_cache(
+    async () => {
+      const sessions = await mergeSessionsByUserId(
+        (uid) =>
+          prisma.movingMotivatorsSession.findMany({
+            where: { userId: uid },
+            select: motivatorListSelect,
+            orderBy: { updatedAt: 'desc' },
+          }),
+        (uid) =>
+          prisma.mMSessionShare.findMany({
+            where: { userId: uid },
+            select: { role: true, createdAt: true, session: { select: motivatorListSelect } },
+          }),
+        userId
+      );
+      const resolved = await batchResolveCollaborators(sessions.map((s) => s.participant));
+      return sessions.map((s) => ({
+        ...s,
+        resolvedParticipant: resolved.get(s.participant.trim()) ?? { raw: s.participant, matchedUser: null },
+      }));
+    },
+    [`motivator-sessions-list-${userId}`],
+    { tags: [sessionsListTag(userId)], revalidate: 60 }
+  )();
 }
 
 /** Sessions owned by team members (where user is team admin) that are NOT shared with the user. */
@@ -48,7 +61,7 @@ export async function getTeamCollaboratorSessionsForAdmin(userId: string) {
     (teamMemberIds, uid) =>
       prisma.movingMotivatorsSession.findMany({
         where: { userId: { in: teamMemberIds }, shares: { none: { userId: uid } } },
-        include: motivatorInclude,
+        select: motivatorListSelect,
         orderBy: { updatedAt: 'desc' },
       }),
     getTeamMemberIdsForAdminTeams,