refactor(frontend): the flat components/ folder moves into shell/, modules/<page>/ and features/<name>/

A pure move (git mv, history kept): 333 files leave components/, which now holds only the platform
layer (ui/) and the legal pages. The shell is the frame (App, header, nav rail, palette, boot); each
page lives in modules/<page>/ with its rail, store and tests; what several pages share sits in
features/<name>/; the shared-link page is watch/. Domain-free helpers went straight to ui/
(ViewSwitcher, FilterRail, the confirm dialog, the language switcher, the copy rows).

Every relative specifier was rewritten (imports, dynamic imports, vi.mock, new URL), and the
contract tests that scan sources now scan the whole app source, not only components/ — each glob
was counted before and after so none went green over fewer files. The locale-format rule matched
`/src/components/` only, so the move would have taken ~300 files out from under its i18n-singleton
check; it now covers every folder that holds components, with a test per folder.

frontend/src/lib/plexImage.contract.test.ts

@@ -53,9 +53,11 @@ it("names each backdrop cut by the width the proxy cuts it at", () => {
 // among the attributes and whatever its variable is called: the first cut of this test read only a
 // leading `src={…thumb…}` and missed two of the three sites it was written for.
 const plexFiles = readSources(__dirname, [
-  "../components/{Plex,plex}*.tsx",
-  "../components/{Home,PosterTile,UpNextCard}.tsx",
-  "!../components/**/*.test.tsx",
+  "../modules/plex/{Plex,plex}*.tsx",
+  "../features/plexCards/{Plex,plex}*.tsx",
+  "../modules/home/Home.tsx",
+  "../modules/plex/{PosterTile,UpNextCard}.tsx",
+  "!../**/*.test.tsx",
 ]);
 const ALLOWED = new Set([
   "plexCards.tsx pic.src", // cardImage's own src (srcSet/sizes beside it): the card cut