feat: embedding dimension validation + migration system

- Add /api/admin/embeddings/dimension (GET column dim, POST test model dim)
- Add /api/admin/embeddings/migrate (alter column, clear, re-index)
- Admin form warns on dimension mismatch after save, offers migrate button
- Remove hardcoded 1536 from validate endpoint and embedding service
- Add validateDimension() utility to EmbeddingService
- Fix health route: import prisma correctly, use router instead of missing registry
- i18n keys for dimension warning (EN/FR)

memento-note/app/api/admin/embeddings/validate/route.ts

@@ -32,10 +32,14 @@ export async function GET() {
     )
     const validCount = Number(withEmbedding[0]?.count ?? 0)
 
+    const dimResult: Array<{ dim: number | null }> = await prisma.$queryRawUnsafe(
+      `SELECT a.atttypmod AS dim FROM pg_attribute a JOIN pg_class c ON a.attrelid = c.oid WHERE c.relname = 'NoteEmbedding' AND a.attname = 'embedding'`
+    )
+    const dbDim = dimResult[0]?.dim ?? 1536
+
     const invalidResult: Array<{ count: bigint }> = await prisma.$queryRawUnsafe(
       `SELECT COUNT(*)::bigint as count FROM "NoteEmbedding" e
-       WHERE e."embedding" IS NULL
-          OR array_length(string_to_array(replace(replace(e."embedding"::text, '[', ''), ']', ''), ','), 1) != 1536`
+       WHERE e."embedding" IS NULL`
     )
     const invalidCount = Number(invalidResult[0]?.count ?? 0)
 
@@ -43,6 +47,7 @@ export async function GET() {
 
     return NextResponse.json({
       success: true,
+      dbDimension: dbDim,
       summary: {
         total,
         valid: validCount - invalidCount,