Show build dates under release build numbers

[x144k]

Build numbers include the date in YYYYMMDD## format, but only the raw number was shown. Now the date appears below each build number, formatted for the user's locale.

The build number itself stays unchanged. The date is rendered as separate text so it doesn't inherit the title style.

Closes #4

[thestinger]

YYYYMMDDNN format in the build number uses the date for UTC time without providing the hour so it can't be used to determine the local date. If it's going to show the date, it needs to make it clear that it's UTC.

[x144k]

Understood. Updated to append (UTC) to make it clear the date is in UTC. Single-line change in Changelog.kt only.