feat: add configurable 12-hour and 24-hour time formats

[anonymoususer72041]

Summary

This PR adds a configurable site-wide time format setting that allows OpenCATS installations to use either 12-hour or 24-hour time display.

This wires the existing site.time_format_24 setting into site localization, session handling, localization settings, the first-run wizard and the installer. It also applies the configured time format across activity display and editing, calendar forms and settings, email template date/time replacement and other user-facing date/time output where appropriate.

The default behavior remains unchanged: existing installations continue to use the 12-hour format unless the 24-hour format is explicitly selected.

Motivation

This improves OpenCATS internationalization by allowing installations to use the time format that matches their locale and users' expectations.

A large share of countries commonly use the 24-hour time format. Supporting both 12-hour and 24-hour formats makes OpenCATS more suitable for international deployments while preserving the existing default behavior for users who prefer the 12-hour format.

[RussH]

PR #812 — Configurable 12-hour / 24-hour time formats

In activity.js, can you re-check the append logic around the date/hour/minutte/eetc fields? It looked like some of the old append code and new conditional append code may both still be present?

[anonymoususer72041]

I re-checked the activity.js append logic around the date/time controls.

In the current branch state, I only see the date, hour and minute controls being appended once. The AM/PM select is created and appended only conditionally for 12-hour mode and the submit path also avoids reading the AM/PM field when it does not exist in 24-hour mode.

I do not see a remaining duplicate append path in the current diff. Could you point me to the specific lines you had in mind if you are still seeing one?