- server: allow distance_unit as an admin default (+ value validation) so the
Admin "Default User Settings" toggle persists instead of returning 400
- i18n: add settings.distance to all 20 locales and translate the labels
through t() instead of hardcoding "Distance"
- route legs: include the unit in the OSRM cache key and recompute on a unit
switch, so map and sidebar distances refresh and never mix units
- keep wind speed tied to the temperature unit — a distance setting must not
silently flip existing Fahrenheit users from mph to km/h
- restore the sub-1km metres reading for metric, convert GPX elevation to feet
for imperial, and format distances with a '.' decimal in every locale
- add units.test.ts
Mirrors the existing temperature_unit pattern. Adds distance_unit to Settings,
a Display settings control, admin default, and a formatDistance helper applied
at distance render sites. Backward compatible (default metric). Closes#1300.
Maurice