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/store/controllers/view-visibility-controller.ts

@@ -0,0 +1,54 @@
+import type {
+    ReactiveController,
+    ReactiveControllerHost,
+} from 'lit';
+import { viewVisibilityStore } from '../view-visibility-store';
+
+/**
+ * ViewVisibilityController connects a Lit component to the
+ * ViewVisibilityStore.
+ *
+ * It reads through to the store rather than copying the map into a
+ * `@state()` field, for the reason `ActiveViewController` does: there
+ * are two live `<app-sidebar>` instances the moment `bottom-nav`'s
+ * "More" drawer opens, and two components holding their own idea of
+ * which destinations exist is how they come to disagree.
+ */
+export class ViewVisibilityController implements ReactiveController {
+    private host: ReactiveControllerHost;
+    private unsubscribe?: () => void;
+
+    constructor(host: ReactiveControllerHost) {
+        this.host = host;
+        host.addController(this);
+    }
+
+    hostConnected(): void {
+        this.unsubscribe = viewVisibilityStore.subscribe(() => {
+            this.host.requestUpdate();
+        });
+
+        void viewVisibilityStore.init();
+    }
+
+    hostDisconnected(): void {
+        this.unsubscribe?.();
+    }
+
+    /** Whether the navigation should offer this destination. */
+    visible(view: string): boolean {
+        return viewVisibilityStore.visible(view);
+    }
+
+    /**
+     * What the config says, ignoring the download-client gate — the
+     * state Settings' own checkbox shows.
+     */
+    enabled(view: string): boolean {
+        return viewVisibilityStore.enabled(view);
+    }
+
+    setVisible(view: string, visible: boolean): Promise<void> {
+        return viewVisibilityStore.setVisible(view, visible);
+    }
+}

frontend/src/store/download-store.ts

@@ -189,6 +189,8 @@ class DownloadStore {
 
     private initialized = false;
 
+    private providersLoaded = false;
+
     constructor() {
         EventsOn(Events.DownloadProvidersChanged, () => {
             void this.refreshProviders();
@@ -285,6 +287,25 @@ class DownloadStore {
         }
     }
 
+    /**
+     * Loads the providers, and only those, once.
+     *
+     * `init()` additionally fetches the descriptors, the downloads and
+     * the request list, which is right for a page about downloading and
+     * wrong for the sidebar: it only needs `available`, to decide
+     * whether the Downloads destination exists at all (#25), and that
+     * is one query. `DownloadProvidersChanged` keeps it current
+     * afterwards, so configuring a client makes the tab appear without
+     * a restart.
+     */
+    async ensureProviders(): Promise<void> {
+        if (this.providersLoaded) return;
+
+        this.providersLoaded = true;
+
+        await this.refreshProviders();
+    }
+
     async refreshProviders(): Promise<void> {
         try {
             this.providersValue = (await ListProviders()) ?? [];

frontend/src/store/view-visibility-store.ts

@@ -0,0 +1,119 @@
+import { EventsOn } from '@runtime/runtime';
+import { GetViewVisibility, SetViewVisible } from '@go/config/config.js';
+import { dictByName } from '@utils/binding';
+import { downloadStore } from './download-store';
+import { Events } from '../events';
+
+type Subscriber = () => void;
+
+/**
+ * Which primary destinations the navigation offers.
+ *
+ * Eleven sidebar entries is more than most libraries need, so #25 makes
+ * them individually toggleable. Three rules about this are load-bearing.
+ *
+ * **Hidden is not unreachable.** This decides what the *nav* draws and
+ * nothing else: `navigate` still resolves a hidden view, which is not a
+ * nicety — detail views navigate into these, and the shell's launch
+ * page is one of them. Nothing here needs a special case for the
+ * highlight either, because #72 moved that onto `active-view-store`:
+ * `app-sidebar` asks `isActive(id)` per *rendered* item, so a hidden
+ * view lights nothing exactly as a detail view does.
+ *
+ * **The defaults live in Go**, in `backend/config.Views`, and this asks
+ * for the *resolved* answer rather than the stored map. A config that
+ * says nothing about a view means "that view's own default", so a copy
+ * of the defaults here would be a second thing to keep in step — and
+ * the one that shipped in the artifact, not the one being edited.
+ *
+ * **Downloads is a second question**, answered by the download client
+ * rather than by the config: a destination for a feature that cannot
+ * work is worse than an absent one. It is gated at `visible()` and not
+ * in the config, so switching it on in Settings still means what it
+ * says once a client exists. `available` is false until the providers
+ * have loaded, which makes the tab *appear* on a fresh launch rather
+ * than appearing and then vanishing — the less jarring half of a race
+ * that resolves in one query.
+ */
+class ViewVisibilityStore {
+    /** The backend's resolved answer, empty until the first load. */
+    private configured: Record<string, boolean> = {};
+
+    private loaded = false;
+
+    private subscribers = new Set<Subscriber>();
+
+    constructor() {
+        EventsOn(Events.GeneralConfigChanged, () => {
+            void this.refresh();
+        });
+
+        // A client configured later has to add the destination without a
+        // restart -- #37's rule, one surface over.
+        downloadStore.subscribe(() => this.notify());
+    }
+
+    /** Loads the visibility map once. Safe to call from every mount. */
+    async init(): Promise<void> {
+        if (this.loaded) return;
+
+        this.loaded = true;
+
+        await Promise.all([
+            this.refresh(),
+            downloadStore.ensureProviders(),
+        ]);
+    }
+
+    /**
+     * Whether the navigation should offer this destination.
+     *
+     * An unknown id is visible: the caller is drawing it from its own
+     * list, and a view this store has not heard of (or has not loaded
+     * yet) is better shown than silently dropped.
+     */
+    visible(view: string): boolean {
+        if (view === 'downloads' && !downloadStore.available) return false;
+
+        return this.configured[view] ?? true;
+    }
+
+    /**
+     * What the *config* says, ignoring the download-client gate — which
+     * is what Settings' own checkbox has to show, or a user with no
+     * client would see Downloads switched off and be unable to switch
+     * it on.
+     */
+    enabled(view: string): boolean {
+        return this.configured[view] ?? true;
+    }
+
+    async setVisible(view: string, visible: boolean): Promise<void> {
+        await SetViewVisible(view, visible);
+
+        // The backend emits GeneralConfigChanged, but the caller is
+        // owed the new state by the time this resolves.
+        await this.refresh();
+    }
+
+    subscribe(fn: Subscriber): () => void {
+        this.subscribers.add(fn);
+
+        return () => this.subscribers.delete(fn);
+    }
+
+    private async refresh(): Promise<void> {
+        try {
+            this.configured = await dictByName(GetViewVisibility());
+            this.notify();
+        } catch (err) {
+            console.error('Failed to load view visibility:', err);
+        }
+    }
+
+    private notify(): void {
+        this.subscribers.forEach((fn) => fn());
+    }
+}
+
+export const viewVisibilityStore = new ViewVisibilityStore();