feat(ui): give every primary view the same page header

Four views had a heading and four did not, two had a sort control and
none showed a count, so the app changed shape as you moved through it
and "how many albums have I got" could only be answered by counting.
The reason they disagreed is that each had written its own arrangement:
the sort toolbar existed three times, in track-list, cover-grid and
playlist-view, as the same twenty lines with different bugs.

<page-header> is that arrangement once - title, count, sort, actions -
and nine views adopt it. Artists and Genres gain the sort control they
never had; Artists sorts by name only, because library.Artist carries
nothing countable, so the header renders a label and a direction button
rather than a select with one option in it. The header keeps its place
while a view loads: a heading that appears only once the data does is
the shifting layout this is meant to stop. The count is omitted, not
zero, until the view has an answer.

The header search box keeps its slot on every view instead of vanishing
on the ones it cannot serve - which is what moved the library filter
and the job indicator on every navigation. It is view-scoped by
decision and now says so: "Search albums" in the placeholder, the scope
named in the header ("Showing artists matching 'tide'"), and disabled
with a reason where there is nothing to search or the page has a search
of its own.

Also fixes an e2e trap this uncovered: the view-lifecycle spec toggled
shuffle and never toggled it back, so a second run against the same app
failed playback.spec's shuffle assertion - a failure that reads exactly
like a regression in whatever you are holding.

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

@@ -19,6 +19,7 @@ import { library } from '@go/models';
 import { LibraryController } from '@store/controllers/library-controller';
 import { libraryStore } from '@store/library-store';
 import { SearchController } from '@store/controllers/search-controller';
+import '@components/page-header/page-header';
 import { queueStore } from '@store/queue-store';
 import {
     ContextMenuController,
@@ -52,6 +53,11 @@ const SCROLL_DEBOUNCE_MS = 100;
 /**
  * Grid entry for the virtualized artist grid.
  */
+const ARTIST_SORT_DIR_KEY = 'artists-view-sort-dir';
+
+/** One key, so the header renders a label and a direction button. */
+const ARTIST_SORT_OPTIONS = [{ id: 'name', label: 'Name' }];
+
 interface ArtistEntry {
     artist: library.Artist;
     index: number;
@@ -184,12 +190,22 @@ export class ArtistsView
         });
     }
 
+    /** Sort direction for the artist grid.
+     *
+     *  There is only one key to sort by: `library.Artist` carries a
+     *  name, an MBID and three image URLs, and nothing countable — so
+     *  the header shows "Sort: Name" and this button, rather than a
+     *  select with one option in it (H-19). */
+    @state()
+    private sortDirection: 'asc' | 'desc' = 'asc';
+
     // -- Memoisation caches for filtered artists --
     private cachedFilteredArtists: library.Artist[] =
         [];
     private cachedGridEntries: ArtistEntry[] = [];
     private prevFilterArtists: library.Artist[] = [];
     private prevFilterTerm = '';
+    private prevFilterDir: 'asc' | 'desc' | '' = '';
 
     /**
      * Recompute the filtered-artists and grid-entries
@@ -202,10 +218,12 @@ export class ArtistsView
 
         if (
             this.artists !== this.prevFilterArtists ||
-            term !== this.prevFilterTerm
+            term !== this.prevFilterTerm ||
+            this.sortDirection !== this.prevFilterDir
         ) {
             this.prevFilterArtists = this.artists;
             this.prevFilterTerm = term;
+            this.prevFilterDir = this.sortDirection;
             this.cachedFilteredArtists =
                 this.computeFilteredArtists();
             this.cachedGridEntries =
@@ -222,15 +240,38 @@ export class ArtistsView
         const term =
             this.searchCtrl.term.toLowerCase();
 
-        if (!term) {
-            return this.artists;
-        }
+        const matching = term
+            ? this.artists.filter((a) =>
+                  a.Name.toLowerCase().includes(term),
+              )
+            : this.artists;
 
-        return this.artists.filter((a) =>
-            a.Name.toLowerCase().includes(term),
+        // Descending is the only reordering available, so ascending
+        // keeps the backend's order rather than re-sorting it: the
+        // array's identity is what tells the virtualizer to repaint,
+        // and copying it every pass would repaint on every keystroke.
+        if (this.sortDirection === 'asc') return matching;
+
+        return [...matching].sort((a, b) =>
+            b.Name.localeCompare(a.Name),
         );
     }
 
+    private onPageHeaderSort = (
+        e: CustomEvent<{ direction: 'asc' | 'desc' }>,
+    ) => {
+        this.sortDirection = e.detail.direction;
+
+        try {
+            localStorage.setItem(
+                ARTIST_SORT_DIR_KEY,
+                this.sortDirection,
+            );
+        } catch {
+            // Ignore storage errors.
+        }
+    };
+
     static override styles = [
         contextMenuStyles,
         css`
@@ -415,9 +456,24 @@ export class ArtistsView
     override connectedCallback() {
         super.connectedCallback();
         this.loadCardSize();
+        this.loadSortDirection();
         this.loadArtists();
     }
 
+    private loadSortDirection() {
+        try {
+            const saved = localStorage.getItem(
+                ARTIST_SORT_DIR_KEY,
+            );
+
+            if (saved === 'asc' || saved === 'desc') {
+                this.sortDirection = saved;
+            }
+        } catch {
+            // Ignore storage errors.
+        }
+    }
+
     override disconnectedCallback() {
         super.disconnectedCallback();
         this.detachWheelListener();
@@ -1334,7 +1390,16 @@ export class ArtistsView
 
     override render() {
         if (this.loading) {
+            // The header keeps its place while the view loads: a
+            // heading that appears only once the data does is the
+            // shifting layout this component exists to stop.
             return html`
+                <page-header
+                    heading="Artists"
+                    .sortOptions=${ARTIST_SORT_OPTIONS}
+                    sort-field="name"
+                    sort-direction=${this.sortDirection}
+                ></page-header>
                 <div class="loading-message">
                     Loading artists...
                 </div>
@@ -1342,15 +1407,18 @@ export class ArtistsView
         }
 
         const entries = this.cachedGridEntries;
-        const searchBar = this.searchCtrl.term
-            ? html`<div class="search-bar-row">
-                  <div class="search-indicator">
-                      Showing results for
-                      &ldquo;${this.searchCtrl
-                          .term}&rdquo;
-                  </div>
-              </div>`
-            : nothing;
+        const searchBar = html`
+            <page-header
+                heading="Artists"
+                .count=${entries.length}
+                count-noun="artist"
+                .sortOptions=${ARTIST_SORT_OPTIONS}
+                sort-field="name"
+                sort-direction=${this.sortDirection}
+                search-term=${this.searchCtrl.term}
+                @sort-change=${this.onPageHeaderSort}
+            ></page-header>
+        `;
 
         if (entries.length === 0) {
             return html`