Introduced a development mode toggle for the app, which, when enabled, displays a distinctive warning on every page to inform users they are viewing a development version of the site. This warning is styled for clear visibility. Development mode is toggled with a new `--dev` command line argument or by setting an environment variable. The change aims to prevent confusion between the development and production environments for both developers and early users.
- Added new CSS rules for a warning alert style in `base.css`.
- Modified `main.py` to check for a development mode flag and pass a warning message to the template if the flag is set.
- Updated `base.html` to include the warning message when present.
- Added a new template for the development warning message.
