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/first-run-wizard/first-run-wizard.ts

@@ -7,6 +7,7 @@ import {
     GetAllLibrariesWithTrackCounts,
 } from '@go/library/Library';
 import { DirectoryPicker } from '@go/frontendutil/FrontendUtil';
+import { describeError, explainError } from '@utils/describe-error';
 
 /**
  * First-run setup wizard.
@@ -236,7 +237,10 @@ export class FirstRunWizard extends LitElement {
 
             if (dir) this.selectedDirectory = dir;
         } catch (err) {
-            this.errorMessage = `Could not open folder picker: ${err}`;
+            this.errorMessage = describeError(
+                err,
+                'The folder picker could not be opened.',
+            );
             console.error('First-run wizard: directory picker failed:', err);
         }
     };
@@ -256,7 +260,10 @@ export class FirstRunWizard extends LitElement {
 
             this.active = false;
         } catch (err) {
-            this.errorMessage = `Could not add the folder: ${err}`;
+            this.errorMessage = explainError(
+                err,
+                'That folder could not be added.',
+            );
             console.error('First-run wizard: add library failed:', err);
         } finally {
             this.saving = false;