Bring back a DB‑independent way to validate/inspect DAGs from the CLI

### Apache Airflow version 3.1.0 ### If "Other Airflow 2/3 version" selected, which one? _No response_ ### What happened? In Airflow 3, commands like airflow dags list and airflow dags list-import-errors rely on the metadata database being populated by a running DAG processor (scheduler/standalone). This removes a lightweight, DB‑independent way to validate DAG parse/import errors and enumerate DAGs directly from the filesystem, which used to be possible in pre‑3.x workflows (e.g., via CLI parsing of DAG_FOLDER without a running processor). Ask: Provide a supported, DB‑independent CLI path to validate and list DAGs/import errors - suitable for local development, pre‑commit hooks, and CI - without requiring the scheduler, processors, or airflow standalone. I initially reported this as #49330 . Now that there is larger consensus that this change was un-intentional. lets bring it back! 😄 cc: @kaxil ### What you think should happen instead? _No response_ ### How to reproduce Seed a basic dag in the dags directory and run. Just use the defaults. ``` airflow db migrate airflow dags list ``` ### Operating System Ubuntu ### Versions of Apache Airflow Providers _No response_ ### Deployment Docker-Compose ### Deployment details _No response_ ### Anything else? _No response_ ### Are you willing to submit PR? - [x] Yes I am willing to submit a PR! ### Code of Conduct - [x] I agree to follow this project's [Code of Conduct](https://github.com/apache/airflow/blob/main/CODE_OF_CONDUCT.md)