MUST-FIX: /api/updates/check now accepts an explicit 'channel' in the POST body;
the Settings dropdown passes the just-picked value to checkUpdatesNow(channel) so
the immediate re-check can't race the debounced autosave PUT and answer for the
previous channel (verified live: body channel wins over stale saved setting).
SHOULD-FIX:
- copy: 'soaked' -> 'soak-tested'; append 'Applies to WebUI updates only.' to the
channel helper text (all 15 locales, native translations)
- mobile: .settings-version-badge gets max-width/overflow/ellipsis in the <=768px
query so the '· Experimental' suffix can't overflow a 320px viewport
(#5 badge-suffix i18n key deferred — non-blocking fast-follow per Fable, matches
the existing English-only version badge on master.)