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/services/view-meta.ts

@@ -0,0 +1,66 @@
+import {
+    ICON_PLAYLIST,
+    ICON_AUTOTAG,
+    ICON_REQUESTED,
+} from '@utils/icon-language';
+
+/** A primary destination. Mirrors `backend/config.View`. */
+export type View =
+    | 'home'
+    | 'playlists'
+    | 'artists'
+    | 'genres'
+    | 'albums'
+    | 'tracks'
+    | 'explore'
+    | 'downloads'
+    | 'autotag'
+    | 'jobs'
+    | 'settings';
+
+export interface ViewMeta {
+    id: View;
+    label: string;
+    icon: string;
+    /**
+     * Views that are never offered as a toggle. Settings alone, because
+     * a user who hides it cannot get back to unhide it.
+     *
+     * This is the *affordance*; the rule is `backend/config.ViewSpec`'s
+     * `Hideable`, which refuses at the setter and drops the key on load.
+     * `config.toml` is hand-editable, so the checkbox being absent is
+     * not what makes this safe — it is only what stops the question
+     * being asked.
+     */
+    alwaysShown?: boolean;
+}
+
+/**
+ * The app's primary destinations, in the order the navigation draws
+ * them and Settings lists them.
+ *
+ * It is here rather than inside `app-sidebar` because #25 gave it a
+ * second reader: Settings renders a toggle per view and needs the same
+ * labels in the same order. Same shape as `services/shortcut-meta.ts`,
+ * which moved out of `config-page` for the same reason -- a private
+ * static that two surfaces need is a private static that is about to be
+ * copied.
+ *
+ * The labels and icons deliberately do not exist in Go. Which views
+ * exist and what an unconfigured install shows is `backend/config.Views`
+ * and is asked for over the binding; how they are *drawn* is the
+ * frontend's, and lives beside the rest of the icon vocabulary.
+ */
+export const VIEW_META: ViewMeta[] = [
+    { id: 'home', label: 'Home', icon: 'house' },
+    { id: 'playlists', label: 'Playlists', icon: ICON_PLAYLIST },
+    { id: 'artists', label: 'Artists', icon: 'user-group' },
+    { id: 'genres', label: 'Genres', icon: 'masks-theater' },
+    { id: 'albums', label: 'Albums', icon: 'compact-disc' },
+    { id: 'tracks', label: 'Tracks', icon: 'music' },
+    { id: 'explore', label: 'Explore', icon: 'globe' },
+    { id: 'downloads', label: 'Downloads', icon: ICON_REQUESTED },
+    { id: 'autotag', label: 'Autotag', icon: ICON_AUTOTAG },
+    { id: 'jobs', label: 'Jobs', icon: 'list-check' },
+    { id: 'settings', label: 'Settings', icon: 'gear', alwaysShown: true },
+];