Wagtail 7.3 upgrade

[nickmoreton]

This PR replaces #257

This pull request updates the project for compatibility with the latest versions of Python, Django, and Wagtail

Framework and Dependency Updates:

• Updated minimum requirements to Django>=5.2 and Wagtail>=7.0

Testing and Compatibility:

• Added testing for Python 3.14, Wagtail 7.2, and 7.3 in tox.ini
• Added new test environments for Wagtail 7.1–7.3.

Codebase Modernization and Cleanup:

• Removed legacy template files and logic for Wagtail <6.0
• Updated URL patterns in wagtail_hooks.py and sandbox/urls.py to use path() instead of re_path(), and switched to Django 2.0+ path converters.
• Updated admin button handling for user listing to support Wagtail 7.1+ and removed legacy code.

Middleware and Configuration Improvements:

• Middleware now supports extending allowed URL names for 2FA bypass via a WAGTAIL_2FA_ALLOWED_URL_NAMES setting.

UI and Template Enhancements:

• Improved device list template button to use consistent Wagtail icon markup.
• Updated authentication form to use formattedfield for better compatibility with modern Wagtail, and improved the sign-out button to use a POST request.

Other minor cleanups include removing the deprecated USE_L10N setting and updating imports for clarity and future compatibility.

[nickmoreton]

The changes here have been combined into #280