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>

src/components/track-note-view.tsx

@@ -0,0 +1,12 @@
+'use client'
+
+import { useEffect } from 'react'
+import { addToRecentlyViewed } from '@/lib/usage'
+
+export function TrackNoteView({ noteId }: { noteId: string }) {
+  useEffect(() => {
+    addToRecentlyViewed(noteId)
+  }, [noteId])
+
+  return null
+}