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/watch.html

@@ -0,0 +1,35 @@
+<!doctype html>
+<html lang="en" data-theme="dark" data-scheme="midnight">
+  <head>
+    <meta charset="utf-8" />
+    <!-- resizes-content: the on-screen keyboard shrinks the layout viewport, not only the visual one,
+         so a dialog's pinned footer (DESIGN C4) sits above the keyboard instead of under it. Chrome's
+         default since 108 only shrinks the visual viewport; Safari ignores the key. -->
+    <meta
+      name="viewport"
+      content="width=device-width, initial-scale=1, interactive-widget=resizes-content"
+    />
+    <link rel="icon" type="image/svg+xml" href="/favicon.svg" />
+    <!-- The public /watch/{token} page's own entry (src/watchMain.tsx), so a shared link does not
+         download the app. Its head mirrors index.html (a contract test holds them equal) — OG:START:
+         the server replaces this block per link so it unfurls with the video's title/thumbnail; an
+         invalid link keeps these generic defaults. -->
+    <!--OG:START-->
+    <title>Siftlode</title>
+    <meta
+      name="description"
+      content="A self-hosted, multi-user reader, subscription organizer and media center with download capabilities."
+    />
+    <meta property="og:title" content="Siftlode" />
+    <meta
+      property="og:description"
+      content="A self-hosted, multi-user reader, subscription organizer and media center with download capabilities."
+    />
+    <meta property="og:type" content="website" />
+    <!--OG:END-->
+  </head>
+  <body>
+    <div id="root"></div>
+    <script type="module" src="/src/watchMain.tsx"></script>
+  </body>
+</html>