feat: MVP-4 Sprint 2 - Co-usage sidebar and search cache

- Add co-usage display to NoteConnections (notas vistas juntas)
- Add search results cache with 50 entry limit and FIFO eviction
- Improve contextual sidebar with usage-based suggestions

src/components/note-connections.tsx

@@ -3,7 +3,7 @@
 import Link from 'next/link'
 import { Card, CardContent, CardHeader, CardTitle } from '@/components/ui/card'
 import { Badge } from '@/components/ui/badge'
-import { ArrowRight, Link2, RefreshCw, ExternalLink } from 'lucide-react'
+import { ArrowRight, Link2, RefreshCw, ExternalLink, Users } from 'lucide-react'
 
 interface BacklinkInfo {
   id: string
@@ -30,6 +30,7 @@ interface NoteConnectionsProps {
   backlinks: BacklinkInfo[]
   outgoingLinks: BacklinkInfo[]
   relatedNotes: RelatedNote[]
+  coUsedNotes: { noteId: string; title: string; type: string; weight: number }[]
 }
 
 function ConnectionGroup({
@@ -84,9 +85,10 @@ export function NoteConnections({
   backlinks,
   outgoingLinks,
   relatedNotes,
+  coUsedNotes,
 }: NoteConnectionsProps) {
   const hasAnyConnections =
-    backlinks.length > 0 || outgoingLinks.length > 0 || relatedNotes.length > 0
+    backlinks.length > 0 || outgoingLinks.length > 0 || relatedNotes.length > 0 || coUsedNotes.length > 0
 
   if (!hasAnyConnections) {
     return null
@@ -136,6 +138,18 @@ export function NoteConnections({
           }))}
           emptyMessage="No hay notas relacionadas"
         />
+
+        {/* Co-used notes - often viewed together */}
+        <ConnectionGroup
+          title="Co-usadas"
+          icon={Users}
+          notes={coUsedNotes.map((cu) => ({
+            id: cu.noteId,
+            title: cu.title,
+            type: cu.type,
+          }))}
+          emptyMessage="No hay notas co-usadas"
+        />
       </CardContent>
     </Card>
   )