perf(watch): a shared link loads the player, not the app

A /watch link is opened by whoever it was sent to — signed out, often on a phone on mobile data —
and it booted through main.tsx: every app provider, the app's i18n (every locale of every area),
the flag sprites, ~392 KB gzip before the player could start. It now has its own HTML entry,
watch.html → watchMain.tsx, which imports WatchPage and what it renders; the server hands every
/watch/ path that page (the OG block injected as before), and vite dev does the same.

Measured on the build: /watch JS 290 → 87 KB gzip, CSS 104 → 19 KB; the app's own bytes unchanged.
Two leaks had to go for that: lib/format imported the app's i18n for one "just now" string (the
relative-time formatters now take `t`, like the file's other t-formatters), and the boundary's
crash copy came from the same i18n (CrashBoundary takes its copy; ErrorBoundary is the app's
wrapper, the watch entry gives it the page's own strings). The page's popover tree went too: it
renders no popover.

Held by: a contract test walking the entry's runtime imports, naming the path to anything only the
app may load (red on a planted i18n import in lib/format), and holding watch.html's head equal to
index.html's; a DB-lane test that every /watch/ path gets the player's page with the link's OG tags
and app paths get the app (red on the old routing). Screenshots at 375 px, EN and HU, video / audio /
password / gone / wrong password / unlocked: identical to the old entry's, bar the video's buffered bar.

frontend/src/components/ui/RelativeTime.tsx

@@ -17,9 +17,10 @@ export function RelativeTime({
   empty?: string;
   className?: string;
 }) {
-  const lang = useTranslation().i18n.language;
+  const { t, i18n } = useTranslation();
+  const lang = i18n.language;
   const ms = typeof at === "number" ? at : at ? new Date(at).getTime() : NaN;
-  const text = Number.isFinite(ms) ? relativeFromMs(ms, lang) : "";
+  const text = Number.isFinite(ms) ? relativeFromMs(ms, lang, t) : "";
   if (!text) return empty ? <span className={className}>{empty}</span> : null;
   const iso = new Date(ms).toISOString();
   return (