feat: MVP-3 Sprint 1 - Usage tracking, smart dashboard, scoring boost

## Registro de Uso
- Nuevo modelo NoteUsage en Prisma
- Tipos de eventos: view, search_click, related_click, link_click, copy_command, copy_snippet
- Funciones: trackNoteUsage, getUsageStats, getRecentlyUsedNotes
- localStorage: recentlyViewed (últimas 10 notas)
- Rastreo de copias en markdown-content.tsx

## Dashboard Rediseñado
- 5 bloques: Recientes, Más usadas, Comandos recientes, Snippets recientes, Según actividad
- Nuevo src/lib/dashboard.ts con getDashboardData()
- Recomendaciones basadas en recentlyViewed

## Scoring con Uso Real
- search.ts: +1 per 5 views (max +3), +2 recency boost
- related.ts: mismo sistema de usage boost
- No eclipsa match textual fuerte

## Tests
- 110 tests pasando (usage, dashboard, related, search)

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

prisma/schema.prisma

@@ -19,6 +19,7 @@ model Note {
   tags       NoteTag[]
   backlinks  Backlink[] @relation("BacklinkTarget")
   outbound   Backlink[] @relation("BacklinkSource")
+  usageEvents NoteUsage[]
 }
 
 model Tag {
@@ -46,3 +47,16 @@ model Backlink {
 
   @@unique([sourceNoteId, targetNoteId])
 }
+
+model NoteUsage {
+  id        String   @id @default(cuid())
+  noteId    String
+  note      Note     @relation(fields: [noteId], references: [id], onDelete: Cascade)
+  eventType String   // 'view' | 'search_click' | 'related_click' | 'link_click'
+  query     String?
+  metadata  String?
+  createdAt DateTime @default(now())
+
+  @@index([noteId, createdAt])
+  @@index([eventType, createdAt])
+}