feat(calendar): add configurable date/time formatting for events

[itsactuallyluna9]

Summary

Adds two new settings, calendar.event_time_format and calendar.event_date_format that control the formatting used for the event card in the calendar panel, with the default option being the previous hardcoded value.

Motivation

I do not use 24-hour time (the default), and would like to be able to configure the event card accordingly. Adding two new fields over reusing the default matches the configuration in other areas of the program.

Type of Change

• Bug fix
• New feature
• Breaking change
• Refactoring
• Build / packaging

Related Issue

Testing

Manually tested on Hyprland.

Manual Coverage

• Tested on Niri
• Tested on Hyprland
• Tested on Sway
• Tested on another compositor:
• Tested with different bar positions and density settings
  • (Read: different control panel sizes)
• Tested at different interface scaling values
• Tested with multiple monitors

Screenshots / Videos

Before

After

Checklist

• This PR is ready for review, or it is marked as Draft.
• I read and followed the relevant guidance in CONTRIBUTING.md.
• I ran just format with clang-format v22+ installed, or this PR has no code changes.
• I ran the relevant build or test commands, or explained why they were not run.
• I self-reviewed the changes.
• I checked for new warnings or errors.
• I will update end-user documentation after merge, or this PR does not change user-facing configuration or behavior.
• I added or updated assets/translations/en.json, or this PR adds no new user-facing strings.
• I did not edit non-English translation files unless this PR is explicitly for translation tooling, an import/export sync, or a maintainer-requested locale change.
• I used the existing canonical names for config keys, IPC names, paths, and identifiers.

Additional Notes