Revert "fix: switch embedding dimension from 1536 to 2560 for qwen-embedding-4b"

This reverts commit e09ea3a145.

memento-note/scripts/migrate-embeddings.ts

@@ -41,7 +41,7 @@ async function main() {
       // Embedding will be generated by the indexNote method which handles pgvector format
       await prisma.$executeRawUnsafe(
         `INSERT INTO "NoteEmbedding" ("id", "noteId", "embedding", "createdAt", "updatedAt")
-         VALUES (gen_random_uuid(), $1, '[0]'::vector(2560), now(), now())
+         VALUES (gen_random_uuid(), $1, '[0]'::vector(1536), now(), now())
          ON CONFLICT ("noteId") DO NOTHING`,
         note.id
       )