fix: make time format user-configurable (12h/24h support)

[tobi-jolly]

What has been changed

• Updated date_time_extension.dart to allow users to choose between 12h and 24h time formats instead of forcing one.

Why it has been changed

• Some users prefer 12h format while others prefer 24h. This change respects the user’s system or app setting.

How it has been changed

• Used use24HourFormat check to decide format dynamically.
• Verified the fix on:
  • Android (emulator)
  • Browser (Chromium based, Microsoft Edge)
  • Browser (Chromium based, Chrome)

Notes

• Code formatted with dart format and imports sorted with dart run import_sorter:main --no-comments.
• Commit follows the Conventional Commits format.

[krille-chan]

This conflicts with the recent changes on e584c22 which fixes the behavior on iOS. This now changes the behavior on iOS to always ignore the user pref. The commit message says this makes it user-configurable, while the user cannot configure anything here (I would vote against such a config anyway)