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/download-picker/download-picker.ts

@@ -9,6 +9,7 @@ import type { DownloadCandidate } from '@store/download-store';
 import { downloadStore } from '@store/download-store';
 import type { download } from '@go/models';
 import './candidate-row';
+import { explainError } from '@utils/describe-error';
 
 /**
  * The "find this album" dialog: searches every enabled download client,
@@ -123,8 +124,17 @@ export class DownloadPicker extends LitElement {
         }
     }
 
+    /**
+     * Monotonic search version. Closing and reopening the dialog for a
+     * different album used to let the first search's result overwrite
+     * the second's (errors.m8); the guard is `explore-view`'s.
+     */
+    private searchVersion = 0;
+
     /** Runs the search that populates the dialog. */
     private async search(): Promise<void> {
+        const version = ++this.searchVersion;
+
         this.searching = true;
         this.errorMessage = '';
         this.candidates = [];
@@ -141,13 +151,23 @@ export class DownloadPicker extends LitElement {
                 expected: this.expected ?? [],
             } as download.SearchRequest);
 
+            if (version !== this.searchVersion) return;
+
             this.downloadId = result.downloadId;
             this.candidates = result.candidates ?? [];
             this.autoPicked = result.autoPicked;
         } catch (err) {
-            this.errorMessage = String(err);
+            if (version !== this.searchVersion) return;
+
+            console.error('download search failed', err);
+            this.errorMessage = explainError(
+                err,
+                'The search did not finish.',
+            );
         } finally {
-            this.searching = false;
+            if (version === this.searchVersion) {
+                this.searching = false;
+            }
         }
     }
 
@@ -161,7 +181,11 @@ export class DownloadPicker extends LitElement {
             await downloadStore.pick(this.downloadId, event.detail.candidateId);
             this.close();
         } catch (err) {
-            this.errorMessage = String(err);
+            console.error('download pick failed', err);
+            this.errorMessage = explainError(
+                err,
+                'That download could not be started.',
+            );
         } finally {
             this.picking = false;
         }