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/app/notes/[id]/page.tsx

@@ -2,6 +2,7 @@ import { prisma } from '@/lib/prisma'
 import { notFound } from 'next/navigation'
 import { getRelatedNotes } from '@/lib/related'
 import { getBacklinksForNote, getOutgoingLinksForNote } from '@/lib/backlinks'
+import { getCoUsedNotes } from '@/lib/usage'
 import { NoteConnections } from '@/components/note-connections'
 import { MarkdownContent } from '@/components/markdown-content'
 import { DeleteNoteButton } from '@/components/delete-note-button'
@@ -36,6 +37,7 @@ export default async function NoteDetailPage({ params }: { params: Promise<{ id:
   const related = await getRelatedNotes(id, 5)
   const backlinks = await getBacklinksForNote(id)
   const outgoingLinks = await getOutgoingLinksForNote(id)
+  const coUsedNotes = await getCoUsedNotes(id, 5)
   const noteType = note.type as NoteType
 
   return (
@@ -100,6 +102,7 @@ export default async function NoteDetailPage({ params }: { params: Promise<{ id:
         backlinks={backlinks}
         outgoingLinks={outgoingLinks}
         relatedNotes={related}
+        coUsedNotes={coUsedNotes}
       />
     </main>
     </>

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>
   )

src/components/search-bar.tsx

@@ -7,6 +7,10 @@ import { Button } from '@/components/ui/button'
 import { Search, Loader2 } from 'lucide-react'
 import { ScoredNote } from '@/lib/search'
 
+// Simple in-memory cache for search results
+const searchCache = new Map<string, ScoredNote[]>()
+const MAX_CACHE_SIZE = 50
+
 export function SearchBar() {
   const [query, setQuery] = useState('')
   const [results, setResults] = useState<ScoredNote[]>([])
@@ -31,14 +35,31 @@ export function SearchBar() {
     }
 
     debounceRef.current = setTimeout(async () => {
+      // Check cache first
+      if (searchCache.has(query)) {
+        setResults(searchCache.get(query)!)
+        setIsOpen(true)
+        setSelectedIndex(-1)
+        return
+      }
+
       setIsLoading(true)
       try {
         const res = await fetch(`/api/search?q=${encodeURIComponent(query)}`)
         const json = await res.json()
         if (json.success) {
-          setResults(json.data.slice(0, 8))
+          const results = json.data.slice(0, 8)
+          setResults(results)
           setIsOpen(true)
           setSelectedIndex(-1)
+
+          // Cache the results
+          if (searchCache.size >= MAX_CACHE_SIZE) {
+            // Remove oldest entry (first in Map)
+            const firstKey = searchCache.keys().next().value
+            if (firstKey) searchCache.delete(firstKey)
+          }
+          searchCache.set(query, results)
         }
       } catch (error) {
         console.error('Search failed:', error)