fix(litellm-pgvector): correct embedding vector dimension 1536 -> 768

schema.prisma hardcoded vector(1536), OpenAI ada-002's size. This stack's
actual embedding model is nomic-embed-text-v1.5, confirmed 768-dim live
against /v1/embeddings. Left as-is, the first insert after a schema push
would fail on a pgvector dimension mismatch.

vendor/litellm-pgvector/prisma/schema.prisma

@@ -30,7 +30,12 @@ model Embedding {
   id              String      @id @default(cuid())
   vector_store_id String
   content         String
-  embedding       Unsupported("vector(1536)")
+  // 768, not OpenAI's ada-002-sized 1536 — this stack's embedding_model is
+  // nomic-embed-text-v1.5 (see docker-compose.yml's embedding-server and
+  // litellm-config.yaml's local-embedding entry), confirmed 768-dim live
+  // against /v1/embeddings. A push with the wrong size here makes every
+  // insert fail on a pgvector dimension mismatch.
+  embedding       Unsupported("vector(768)")
   metadata        Json?
   created_at      DateTime    @default(now())