refactor(frontend): the module stores mount from the registry, and the feed and Plex each own their saved views

A module's definition names its store (feed: filters, view, saved views; Plex: browse state, saved
views; channels, files, playlists their provider), and ModuleStores mounts them at the root in
registry order instead of a hand-nested tree in main.tsx. A contract test holds that every store's
read side is in reach and that no store's static imports leave its own module, so the order cannot
matter.

Saved views were one provider that switched between the feed and Plex by the active page and reset
on each switch. The logic is now one hook (useSavedViewsStore) with an instance per module; the
shared chip, popover and modal read the views their page or rail hands down. A feed view applied
and edited now survives a visit to Plex. Plex's views are still asked for only on its page, and a
module's manage modal still closes when its page is left. The feed's URL-override check applies
only on the feed page, where its filter params live.

The Channels store's tab type moves from the page into the store's context.

CLAUDE.md

@@ -76,8 +76,9 @@ cannot (an ORM write on another unit's loaded row, SQL in `text()`, a commit by
 Frontend, by folder under `src/`: `main.tsx` provider tree → `shell/` (`App`, header, nav rail, palette,
 boot; a shared `/watch` link boots from its own entry, `watch.html` → `watchMain.tsx` → `watch/`, held
 app-free by a contract test) → **`modules/<page>/`** (one folder per page: the page, its rail, its store, its tests,
-and its `module.ts` definition — label, icon, gate, the lazy page and rail — collected in nav order by
-`features/navigation/moduleRegistry`; a new page is its folder, its id in `lib/urlState` and one line there) →
+and its `module.ts` definition — label, icon, gate, the lazy page and rail, its store — collected in nav order by
+`features/navigation/moduleRegistry`, which also mounts every store at the root; a new page is its folder, its id in
+`lib/urlState` and one line there) →
 **`features/<name>/`** (what several pages share: video cards, filters, downloads, the player, navigation) → the
 **platform layer `components/ui/`** (domain-free primitives: the popover engine and its menus, `Modal`/`Overlay`,
 `Button`/`form`, `DataTable`/`VirtualGrid`, `QueryState`,