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/AdminLogs.tsx

@@ -11,7 +11,7 @@ import { Copy, Radio, Search } from "lucide-react";
 
 import { api, type LogFacet, type LogQuery, type ServerLogRow } from "../lib/api";
 import { copyText } from "../lib/clipboard";
-import { formatDateTime } from "../lib/format";
+import { formatDateTimeSec } from "../lib/format";
 import { nextNavId, notifyNav, rememberNavPosition } from "../lib/history";
 import { LEVEL_GROUPS, type LevelGroup } from "../lib/log";
 import {
@@ -406,7 +406,7 @@ export default function AdminLogs() {
                     level={row.level}
                     event={row.event ?? "—"}
                     msg={row.msg}
-                    title={formatDateTime(row.ts)}
+                    title={formatDateTimeSec(row.ts)}
                     open={open === row.id}
                     onToggle={() => setOpen(open === row.id ? null : row.id)}
                   >
@@ -475,7 +475,7 @@ function RowDetail({
     <div className="flex flex-col gap-2">
       <dl className="grid grid-cols-[max-content_minmax(0,1fr)] gap-x-3 gap-y-0.5 font-sans text-xs">
         <dt>{t("adminLogs.fields.when")}</dt>
-        <dd className="tabular-nums">{formatDateTime(row.ts)}</dd>
+        <dd className="tabular-nums">{formatDateTimeSec(row.ts)}</dd>
         <dt>{t("adminLogs.fields.source")}</dt>
         <dd className="font-mono">
           {row.source} · {row.logger}