chore: align forest AI development setup

backend/etc/agent.dev.yaml

@@ -1,6 +1,7 @@
+# 仅供本地开发使用；以下默认凭据与密钥不得用于生产环境。
 env: development
 port: "9150"
-dsn: "postgres://postgres:postgres@localhost:5432/agent_dev?sslmode=disable"
+dsn: "postgres://agent:agent@localhost:5432/agent?sslmode=disable"
 storage_dir: "./data/files"
 max_upload_bytes: 33554432
 auth_secret: "development-auth-secret-change-me"