fix(migrations): renumber model_id uniqueness migration to 0013

db/migrations/0013_model_id_unique_per_provider.up.sql

@@ -0,0 +1,15 @@
+-- 0013_model_id_unique_per_provider
+-- Change model_id uniqueness from global to per provider.
+
+DO $$
+BEGIN
+  IF EXISTS (SELECT 1 FROM pg_constraint WHERE conname = 'models_model_id_unique') THEN
+    ALTER TABLE models DROP CONSTRAINT models_model_id_unique;
+  END IF;
+
+  IF NOT EXISTS (SELECT 1 FROM pg_constraint WHERE conname = 'models_provider_model_id_unique') THEN
+    ALTER TABLE models
+      ADD CONSTRAINT models_provider_model_id_unique UNIQUE (llm_provider_id, model_id);
+  END IF;
+END
+$$;