refactor(config)!: use static defaults + useTwelveHourClock -> clockFormat (#2032)

* refactor(config): use static default for weather units

Use a static enum value, then resolve the real unit at runtime

* refactor(config)!: useTwelveHourClock -> clockFormat

Use an enum instead of a bool so we can have a static default, using the
same pattern as the weather units