refactor(frontend): adopt the lifecycle and the notification surface

The remaining views, brought onto the two mechanisms added earlier in
this series.

The lifecycle: every cached primary view moves its document listeners,
intervals and event subscriptions off connect/disconnect and onto
`viewActivated`/`viewDeactivated`, so `autotag-view` stops fielding
keystrokes from Settings, `downloads-view`'s 30 s clock stops ticking
for the session, and an off-screen view stops rendering on every
search keystroke. `autotag-view` keeps a document listener only for
Escape, whose dialogs Phase 5 migrates to wa-dialog anyway.

The voice: the silent failures now speak — scan and full rescan (with
a guard against the double-click the coalescing window allowed), job
pause/resume/cancel, playlist delete, download request pause/remove/
clear, add and rename library, add-to-playlist, playlist track
removal, autotag's dialogs and its apply, and favourite reverts. Both
private toasts are gone, along with their CSS and keyframes. Playlist
delete (single and the multi-select loop), download-request removal,
download-client removal and a queue clear over 20 tracks ask first.

Loading, empty and failed become three states rather than one, in
`track-list` and `genre-details` — the first is on the first screen a
new user ever sees — and the Settings index panel seeds itself with
`GetIndexStatus()` instead of waiting forever for a change event.
`smart-playlist-editor` and `download-picker` take the request-version
guard `explore-view` already had.

`track-details` loads through one memoised dynamic import in all ten
openers, which is what takes its 42 kB out of the startup chunk: an
un-upgraded custom element is a real HTMLElement on which `?.show()`
throws, so each opener awaits it before touching the element its
template already rendered.

frontend/src/components/home-view/home-view.ts

@@ -10,6 +10,7 @@ import { libraryStore } from '@store/library-store';
 import { EventsOn } from '@runtime/runtime';
 import { Events } from '../../events';
 import { designTokens } from '../../styles/tokens.css';
+import { ViewLifecycleMixin } from '../../utils/view-lifecycle';
 
 type Shelf = home.Shelf;
 
@@ -36,7 +37,7 @@ const KIND_ICONS: Record<string, string> = {
  * cover do the two things a cover should: open the album, or play it.
  */
 @customElement('home-view')
-export class HomeView extends LitElement {
+export class HomeView extends ViewLifecycleMixin(LitElement) {
     @state() private shelves: Shelf[] = [];
 
     @state() private loading = true;
@@ -194,8 +195,10 @@ export class HomeView extends LitElement {
         `,
     ];
 
-    override connectedCallback(): void {
-        super.connectedCallback();
+    protected override onViewActivate(): void {
+        // Reloaded on arrival rather than kept live: the shelves are a
+        // judgement about the whole library, so the answer while the
+        // page is off screen is of no interest to anyone.
         void this.load();
 
         // A finished scan changes what every shelf would say, and the
@@ -204,12 +207,10 @@ export class HomeView extends LitElement {
         this.unsubScan = EventsOn(Events.LibraryScanComplete, () => {
             void this.load();
         });
-    }
-
-    override disconnectedCallback(): void {
-        super.disconnectedCallback();
-        this.unsubScan?.();
-        this.unsubScan = undefined;
+        this.whileActive(() => {
+            this.unsubScan?.();
+            this.unsubScan = undefined;
+        });
     }
 
     /**