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/src/components/bottom-nav/bottom-nav.ts

@@ -8,6 +8,7 @@ import '../sidebar/app-sidebar.js';
 import { nameDialog } from '@utils/name-dialog';
 import { ICON_PLAYLIST } from '@utils/icon-language';
 import { ActiveViewController } from '@store/controllers/active-view-controller';
+import { ViewVisibilityController } from '@store/controllers/view-visibility-controller';
 
 type View = 'home' | 'albums' | 'tracks' | 'playlists';
 
@@ -129,6 +130,22 @@ export class BottomNav extends LitElement {
      */
     private activeCtrl = new ActiveViewController(this);
 
+    /**
+     * The tab bar honours the sidebar's toggles (#25), and the reason is
+     * inside this component rather than a general rule about phones.
+     * `PHONE_COLUMN_IDS` is the precedent for "what a phone shows is a
+     * different question", and it would apply here too -- except that
+     * "More" opens the *same* `<app-sidebar>`, which filters. An
+     * unfiltered bar would therefore contradict its own drawer, one tap
+     * apart, and a destination the user switched off is off wherever it
+     * is offered.
+     *
+     * Which four tabs remains plan 016's committed subset; this only
+     * removes from it. Hiding all four leaves "More", which is always
+     * present and reaches everything.
+     */
+    private visibilityCtrl = new ViewVisibilityController(this);
+
     /**
      * Whether the drawer has been asked for.
      *
@@ -211,7 +228,9 @@ export class BottomNav extends LitElement {
         return html`
             <nav aria-label="Primary">
                 <ul>
-                    ${BottomNav.TABS.map((tab) => html`
+                    ${BottomNav.TABS
+                        .filter((tab) => this.visibilityCtrl.visible(tab.id))
+                        .map((tab) => html`
                         <li>
                             <button
                                 type="button"