feat(dashboard): tableau de bord Second Brain configurable avec chargement progressif

Briefing granulaire, pistes rapides puis enrichissement async, layout persisté v5,
suggestions agents, intégration Gmail et navigation sidebar alignée sur /home.

Co-authored-by: Cursor <cursoragent@cursor.com>

memento-note/app/api/clusters/route.ts

@@ -20,8 +20,54 @@ export async function GET(request: NextRequest) {
 
     // Check for stored results (even if stale/périmés)
     const stored = await clusteringService.getStoredClusters(userId)
+    const lite = request.nextUrl.searchParams.get('lite') === '1'
+
     if (stored) {
       const cached = stored.clusters
+
+      if (lite) {
+        const [bridgeNotesData, totalNotes] = await Promise.all([
+          prisma.bridgeNote.findMany({
+            where: { userId },
+            orderBy: { bridgeScore: 'desc' },
+            take: 5,
+            select: { noteId: true, bridgeScore: true, clustersConnected: true },
+          }),
+          prisma.note.count({ where: { userId, trashedAt: null } }),
+        ])
+
+        let enrichedBridgeNotes: object[] = []
+        if (bridgeNotesData.length > 0) {
+          const bridgeNoteDetails = await prisma.note.findMany({
+            where: { id: { in: bridgeNotesData.map(b => b.noteId) } },
+            select: { id: true, title: true },
+          })
+          const bridgeNoteDetailsMap = new Map(bridgeNoteDetails.map(n => [n.id, n]))
+
+          enrichedBridgeNotes = bridgeNotesData.map(b => {
+            const clustersConnected = JSON.parse(b.clustersConnected) as number[]
+            return {
+              noteId: b.noteId,
+              bridgeScore: b.bridgeScore,
+              clustersConnected,
+              clusterNames: clustersConnected.map(
+                cid => cached.find(c => c.clusterId === cid)?.name || `Cluster ${cid}`,
+              ),
+              note: bridgeNoteDetailsMap.get(b.noteId),
+            }
+          })
+        }
+
+        return NextResponse.json({
+          clusters: cached,
+          bridgeNotes: enrichedBridgeNotes,
+          cached: true,
+          stale: stored.stale,
+          lastCalculated: stored.lastCalculated,
+          totalNotes,
+        })
+      }
+
       // Fetch notes with their cluster assignments
       const notes = await prisma.note.findMany({
         where: { userId, trashedAt: null },