feat(design): the Copy rule — names, verbs, dates and units (E28 S3g)

The owner's picks (all the recommended options) become DESIGN.md's Copy
chapter and a sweep of both languages (742 values, no key drift):

- One name per feature: the rail's label, which may shorten it (Alerts
  -> Notifications, Fiókok -> Felhasználók, Download Center -> Downloads,
  Channel manager -> Channels); one "sync from YouTube" verb.
- Four verbs, four meanings (Delete / Remove / Dismiss / Discard, and
  their Hungarian pairs), checked against what each action does.
- Sentence case, the app's places capitalised; "…" on a command that
  asks first (a popover or form title got its own key without it);
  one-sentence messages without a stop or a tick, "Couldn't …"; curly
  quotes.
- Dates only from lib/format.ts, in the UI language: formatDateTime
  names the month and stops at the minute (it printed "9/27/2026,
  8:30:14 AM"), formatDateTimeSec for the log, the audit and the
  recorder; ui/RelativeTime pairs "3d ago" with the exact minute on
  hover. local/date-format refuses toLocale*String and Intl date
  formatters elsewhere.
- Units from Intl, short (formatUnit): runtimes, totals, the Scheduler
  countdown, the stats range, the player's tap skip. "2h 13m" was
  English in both languages.
- src/i18n/copyRule.test.ts holds the machine-readable part (quotes,
  "...", ticks, bare unit letters).

frontend/src/components/Scheduler.tsx

@@ -22,7 +22,7 @@ import { useLiveQuery } from "../lib/useLiveQuery";
 import { Button } from "./ui/Button";
 import { LoadingState, StateMessage } from "./ui/QueryState";
 import { useConfirm } from "./confirmContext";
-import { formatNumber, relativeTime } from "../lib/format";
+import { formatDateTime, formatNumber, formatUnit, relativeTime } from "../lib/format";
 import { notify } from "../lib/notifications";
 import Tooltip from "./ui/Tooltip";
 import { notifyActionError } from "../lib/actionErrors";
@@ -48,11 +48,12 @@ function secsUntil(iso: string | null): number | null {
 
 function fmtCountdown(s: number): string {
   if (s <= 0) return i18n.t("time.eta.now");
-  if (s < 60) return `${s}s`;
+  // The countdown speaks the UI language's units (DESIGN Copy), like every other duration.
+  if (s < 60) return formatUnit(s, "second");
   const m = Math.floor(s / 60);
-  if (m < 60) return `${m}m ${s % 60}s`;
+  if (m < 60) return `${formatUnit(m, "minute")} ${formatUnit(s % 60, "second")}`;
   const h = Math.floor(m / 60);
-  return `${h}h ${m % 60}m`;
+  return `${formatUnit(h, "hour")} ${formatUnit(m % 60, "minute")}`;
 }
 
 const DOT_CLASS: Record<string, string> = {
@@ -243,7 +244,10 @@ function JobRow({
             </Tooltip>
           )}
         </div>
-        <div className="text-2xs text-muted truncate">
+        <div
+          className="text-2xs text-muted truncate"
+          title={(!job.running && formatDateTime(job.last_finished)) || undefined}
+        >
           {job.running
             ? t("scheduler.runningNow")
             : job.last_finished