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/lib/ai/services/embedding.service.ts

@@ -6,6 +6,7 @@
 
 import { withAiProviderFallback } from '../fallback'
 import { getSystemConfig } from '@/lib/config'
+import { prisma } from '@/lib/prisma'
 
 export interface EmbeddingResult {
   embedding: number[]
@@ -14,7 +15,6 @@ export interface EmbeddingResult {
 }
 
 export class EmbeddingService {
-  private readonly EMBEDDING_DIMENSION = 1536
   private readonly MAX_CHARS = 15000
 
   private truncateForEmbedding(text: string): string {
@@ -109,6 +109,38 @@ export class EmbeddingService {
    * Check if a note needs embedding regeneration.
    * Uses a content-content comparison (not embedding-content).
    */
+  async getDbDimension(): Promise<number | null> {
+    try {
+      const result: 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'`
+      )
+      return result[0]?.dim ?? null
+    } catch {
+      return null
+    }
+  }
+
+  async getModelDimension(): Promise<number | null> {
+    try {
+      const { dimension } = await this.generateEmbedding('dimension test')
+      return dimension
+    } catch {
+      return null
+    }
+  }
+
+  async validateDimension(): Promise<{ dbDimension: number | null; modelDimension: number | null; match: boolean }> {
+    const [dbDimension, modelDimension] = await Promise.all([
+      this.getDbDimension(),
+      this.getModelDimension(),
+    ])
+    return {
+      dbDimension,
+      modelDimension,
+      match: dbDimension !== null && modelDimension !== null && dbDimension === modelDimension,
+    }
+  }
+
   shouldRegenerateEmbedding(
     noteContent: string,
     _lastEmbeddingContent: string | null,