fix: improve note interactions and markdown LaTeX support

## Bug Fixes

### Note Card Actions
- Fix broken size change functionality (missing state declaration)
- Implement React 19 useOptimistic for instant UI feedback
- Add startTransition for non-blocking updates
- Ensure smooth animations without page refresh
- All note actions now work: pin, archive, color, size, checklist

### Markdown LaTeX Rendering
- Add remark-math and rehype-katex plugins
- Support inline equations with dollar sign syntax
- Support block equations with double dollar sign syntax
- Import KaTeX CSS for proper styling
- Equations now render correctly instead of showing raw LaTeX

## Technical Details

- Replace undefined currentNote references with optimistic state
- Add optimistic updates before server actions for instant feedback
- Use router.refresh() in transitions for smart cache invalidation
- Install remark-math, rehype-katex, and katex packages

## Testing

- Build passes successfully with no TypeScript errors
- Dev server hot-reloads changes correctly

keep-notes/app/api/admin/embeddings/validate/route.ts

@@ -0,0 +1,100 @@
+import { NextResponse } from 'next/server'
+import prisma from '@/lib/prisma'
+import { auth } from '@/auth'
+import { validateEmbedding } from '@/lib/utils'
+
+/**
+ * Admin endpoint to validate all embeddings in the database
+ * Returns a list of notes with invalid embeddings
+ */
+export async function GET() {
+  try {
+    const session = await auth()
+    if (!session?.user?.id) {
+      return NextResponse.json({ error: 'Unauthorized' }, { status: 401 })
+    }
+
+    // Check if user is admin
+    const user = await prisma.user.findUnique({
+      where: { id: session.user.id },
+      select: { role: true }
+    })
+
+    if (!user || user.role !== 'ADMIN') {
+      return NextResponse.json({ error: 'Forbidden - Admin only' }, { status: 403 })
+    }
+
+    // Fetch all notes with embeddings
+    const allNotes = await prisma.note.findMany({
+      select: {
+        id: true,
+        title: true,
+        embedding: true
+      }
+    })
+
+    const invalidNotes: Array<{
+      id: string
+      title: string
+      issues: string[]
+    }> = []
+
+    let validCount = 0
+    let missingCount = 0
+    let invalidCount = 0
+
+    for (const note of allNotes) {
+      // Check if embedding is missing
+      if (!note.embedding) {
+        missingCount++
+        invalidNotes.push({
+          id: note.id,
+          title: note.title || 'Untitled',
+          issues: ['Missing embedding']
+        })
+        continue
+      }
+
+      // Parse and validate embedding
+      try {
+        const embedding = JSON.parse(note.embedding)
+        const validation = validateEmbedding(embedding)
+
+        if (!validation.valid) {
+          invalidCount++
+          invalidNotes.push({
+            id: note.id,
+            title: note.title || 'Untitled',
+            issues: validation.issues
+          })
+        } else {
+          validCount++
+        }
+      } catch (error) {
+        invalidCount++
+        invalidNotes.push({
+          id: note.id,
+          title: note.title || 'Untitled',
+          issues: [`Failed to parse embedding: ${error}`]
+        })
+      }
+    }
+
+    return NextResponse.json({
+      success: true,
+      summary: {
+        total: allNotes.length,
+        valid: validCount,
+        missing: missingCount,
+        invalid: invalidCount
+      },
+      invalidNotes
+    })
+  } catch (error) {
+    console.error('[EMBEDDING_VALIDATION] Error:', error)
+    return NextResponse.json(
+      { success: false, error: String(error) },
+      { status: 500 }
+    )
+  }
+}