Simplify to single 'default' backend name

- Replace kvstore/sqlstore backend names with unified 'default'
- Context-aware parsing handles KVStore vs SqlStore based on usage
- Provider configs use 'backend: default' everywhere
- Much cleaner: kvstore { backend: default } instead of { backend: kvstore }

llama_stack/distributions/postgres-demo/run.yaml

@@ -73,14 +73,7 @@ providers:
     provider_type: remote::model-context-protocol
 persistence:
   backends:
-    kvstore:
-      type: postgres
-      host: ${env.POSTGRES_HOST:=localhost}
-      port: ${env.POSTGRES_PORT:=5432}
-      db: ${env.POSTGRES_DB:=llamastack}
-      user: ${env.POSTGRES_USER:=llamastack}
-      password: ${env.POSTGRES_PASSWORD:=llamastack}
-    sqlstore:
+    default:
       type: postgres
       host: ${env.POSTGRES_HOST:=localhost}
       port: ${env.POSTGRES_PORT:=5432}
@@ -89,9 +82,9 @@ persistence:
       password: ${env.POSTGRES_PASSWORD:=llamastack}
   stores:
     metadata:
-      backend: kvstore
+      backend: default
     inference:
-      backend: sqlstore
+      backend: default
 models:
 - metadata: {}
   model_id: ${env.INFERENCE_MODEL}