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/track-details/track-details.ts

@@ -22,7 +22,7 @@ import { GetTrackMBIDs } from '@go/library/Library';
 type TrackMBIDs = library.TrackMBIDs;
 import { ImageFilePicker, ReadFile } from '@go/frontendutil/FrontendUtil';
 import { libraryStore } from '../../store/library-store';
-import { EventsOn, EventsOff } from '@runtime/runtime';
+import { EventsOn } from '@runtime/runtime';
 import { Events } from '../../events';
 
 import '@awesome.me/webawesome/dist/components/dialog/dialog.js';
@@ -1714,8 +1714,10 @@ export class TrackDetails extends LitElement {
 
         const changes = this.buildBatchChanges();
 
-        // Listen for progress events.
-        EventsOn(
+        // Listen for progress events. Kept as the unsubscribe function
+        // EventsOn returns, rather than EventsOff(name), which removes
+        // *every* listener for that event (errors.p3).
+        const stopProgress = EventsOn(
             Events.BatchWriteProgress,
             (data: {
                 current: number;
@@ -1762,7 +1764,7 @@ export class TrackDetails extends LitElement {
                 ],
             };
         } finally {
-            EventsOff(Events.BatchWriteProgress);
+            stopProgress();
             this.batchProgress = null;
         }
     };