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/lib/format.ts

@@ -1,5 +1,4 @@
 import type { TFunction } from "i18next";
-import i18n from "../i18n";
 
 // The one home of the app's LOCALE forms — numbers, units, dates (alphabetical order: `collate.ts`) —
 // all in the UI language, never the browser's (lint: `local/locale-format` refuses a hand-built one elsewhere).
@@ -8,7 +7,9 @@ import i18n from "../i18n";
 // the React Compiler memoizes a call on its arguments, so a formatter that read the language
 // off the i18n singleton kept its old answer after a language switch — a card still said "2 hr 4 min"
 // beside a hero saying "2 ó 16 p". Passing `i18n.language` (from useTranslation) makes the language a
-// dependency the compiler can see; the signature makes forgetting it a type error.
+// dependency the compiler can see; the signature makes forgetting it a type error. It is also why
+// this file never imports the app's i18n: the public /watch entry formats a file size through it, and
+// that import alone carried every locale of every area into the page a shared link opens.
 
 // Intl formatters are expensive to build and every grid formats one per card: one per language ×
 // options, built lazily. Keyed by language because the user can switch it at runtime.
@@ -23,9 +24,9 @@ function numberFormat(lang: string, opts: Intl.NumberFormatOptions = {}): Intl.N
   return f;
 }
 
-export function relativeTime(iso: string | null, lang: string): string {
+export function relativeTime(iso: string | null, lang: string, t: TFunction): string {
   if (!iso) return "";
-  return relativeFromMs(new Date(iso).getTime(), lang);
+  return relativeFromMs(new Date(iso).getTime(), lang, t);
 }
 
 /** Human file size, binary units (1024), the number in the UI language: 501747 -> "490 KB",
@@ -90,11 +91,11 @@ function relativeFormatter(lang: string): Intl.RelativeTimeFormat {
  * client-side notifications whose timestamps are already numbers). One implementation shared
  * instead of re-implemented per component. Empty string for a timestamp that can't be read, so a
  * caller's `|| "—"` fallback covers it like a missing one. */
-export function relativeFromMs(ms: number, lang: string): string {
+export function relativeFromMs(ms: number, lang: string, t: TFunction): string {
   const secs = Math.max(0, (Date.now() - ms) / 1000);
   if (!Number.isFinite(secs)) return "";
   // Sub-minute is the one case Intl has no wording for — it would say "0m ago".
-  if (secs < RELATIVE_UNITS[0][0]) return i18n.t("time.justNow", { lng: lang });
+  if (secs < RELATIVE_UNITS[0][0]) return t("time.justNow", { lng: lang });
   let [div, unit] = RELATIVE_UNITS[0];
   for (const [unitSecs, unitName] of RELATIVE_UNITS) {
     if (secs < unitSecs) break;