feat(shell): draw only the destinations the user kept

The navigation reads the resolved map from the backend rather than
holding a copy of the defaults, which would be the copy that shipped in
the binary rather than the one being edited.

Hiding takes away the nav item and nothing else: `navigate` still
resolves a hidden view, which detail views and the launch page depend
on. No special case was needed for the highlight, because #72 moved
that onto `active-view-store` -- the sidebar asks `isActive(id)` per
*rendered* item, so a hidden view lights nothing exactly as a detail
view does.

Downloads is gated at the nav on `downloadStore.available` rather than
in the config, so switching it on in Settings still means what it says
once a client exists, and the tab appears without a restart. `available`
is false until the providers have loaded, which makes the item appear on
a fresh launch rather than appearing and then vanishing.

The tab bar honours the toggles too, and the reason is local rather than
a general rule about phones: "More" opens the *same* `<app-sidebar>`,
which filters, so an unfiltered bar would contradict its own drawer one
tap away. Which four tabs is still plan 016's subset; this only removes
from it, and "More" is never filtered.

`services/view-meta.ts` is the destination list, on `shortcut-meta.ts`'s
pattern, because Settings is now a second reader of the same labels in
the same order.

Two existing sidebar tests had to say which world they describe: eleven
destinations now assumes a configured download client.

frontend/test/components/chrome.test.ts

@@ -26,7 +26,26 @@ import {
   ICON_REQUESTED,
 } from '@utils/icon-language';
 
+/** A configured, enabled download client. */
+const PROVIDER = {
+  id: 1,
+  kind: 'slskd',
+  name: 'Sound',
+  enabled: true,
+  priority: 50,
+};
+
 describe('<app-sidebar>', () => {
+  // Downloads is offered only where there is a client to download with
+  // (#25), so "all eleven destinations" is a statement about a
+  // configured install. `view-visibility.test.ts` owns the rule itself;
+  // this states the world these cases are describing.
+  beforeEach(async () => {
+    stub('download.Service.ListProviders', [PROVIDER]);
+    emit(Events.DownloadProvidersChanged);
+    await flush();
+  });
+
   it('renders a testid per destination, which is how e2e navigates', async () => {
     const el = await fixture('app-sidebar');