fix(flutter): library Artists tab 404 + Albums tab 3-up grid

Artists tab 404: client called /api/library/artists, but the server
mounts the artists list at /api/artists (handleListArtists). Albums
sit at /api/library/albums for historical reasons — the paths aren't
symmetric. Switch listArtists() to /api/artists with sort=alpha.

Albums tab grid: matched the responsive 3-up layout we built for
artist detail. LayoutBuilder computes cellW from available width;
AlbumCard sized to the cell with titleMaxLines: 2; mainAxisExtent
matches actual content height (cover + 2-line title + artist line +
fudge). No more wide-aspect cells with empty space below the card.

Also wired `extra: ref` on the artists/albums grids and the Liked
tab so detail-screen nav hydration kicks in here too — taps from
library screens get the same instant header that home tiles do.

flutter_client/lib/api/endpoints/library_lists.dart

@@ -12,9 +12,16 @@ class LibraryListsApi {
   final Dio _dio;
 
   Future<Paged<ArtistRef>> listArtists({int limit = 50, int offset = 0}) async {
+    // Server mounts the artists list at /api/artists (handleListArtists),
+    // not /api/library/artists. Albums use /api/library/albums for
+    // historical reasons; the paths aren't symmetric.
     final r = await _dio.get<Map<String, dynamic>>(
-      '/api/library/artists',
-      queryParameters: {'limit': limit, 'offset': offset},
+      '/api/artists',
+      queryParameters: {
+        'limit': limit,
+        'offset': offset,
+        'sort': 'alpha',
+      },
     );
     return Paged.fromJson(r.data ?? const {}, ArtistRef.fromJson);
   }

flutter_client/lib/library/library_screen.dart

@@ -144,10 +144,14 @@ class _ArtistsTab extends ConsumerWidget {
                       childAspectRatio: 0.78,
                     ),
                     itemCount: page.items.length,
-                    itemBuilder: (ctx, i) => ArtistCard(
-                      artist: page.items[i],
-                      onTap: () => ctx.push('/artists/${page.items[i].id}'),
-                    ),
+                    itemBuilder: (ctx, i) {
+                      final artist = page.items[i];
+                      return ArtistCard(
+                        artist: artist,
+                        onTap: () => ctx.push('/artists/${artist.id}',
+                            extra: artist),
+                      );
+                    },
                   ),
                 ),
         );
@@ -167,20 +171,41 @@ class _AlbumsTab extends ConsumerWidget {
               ? Center(child: Text("No albums yet — scan a library folder via the server's config.", style: TextStyle(color: fs.ash), textAlign: TextAlign.center))
               : RefreshIndicator(
                   onRefresh: () async => ref.refresh(_libraryAlbumsProvider.future),
-                  child: GridView.builder(
-                    padding: const EdgeInsets.all(8),
-                    gridDelegate: const SliverGridDelegateWithFixedCrossAxisCount(
-                      crossAxisCount: 2,
-                      mainAxisSpacing: 8,
-                      crossAxisSpacing: 8,
-                      childAspectRatio: 0.78,
-                    ),
-                    itemCount: page.items.length,
-                    itemBuilder: (ctx, i) => AlbumCard(
-                      album: page.items[i],
-                      onTap: () => ctx.push('/albums/${page.items[i].id}'),
-                    ),
-                  ),
+                  // Same responsive 3-up grid as the artist detail
+                  // album list — LayoutBuilder + AlbumCard sized to the
+                  // cell, mainAxisExtent matched to actual card height.
+                  child: LayoutBuilder(builder: (ctx, constraints) {
+                    const cols = 3;
+                    const sidePad = 8.0;
+                    const gap = 8.0;
+                    final cellW = (constraints.maxWidth -
+                            sidePad * 2 -
+                            gap * (cols - 1)) /
+                        cols;
+                    // cover (cellW - 16) + gap (8) + 2-line title (~36)
+                    // + artist line (~16) + small fudge.
+                    final cellH = (cellW - 16) + 8 + 36 + 16 + 4;
+                    return GridView.builder(
+                      padding: const EdgeInsets.all(sidePad),
+                      gridDelegate: SliverGridDelegateWithFixedCrossAxisCount(
+                        crossAxisCount: cols,
+                        mainAxisExtent: cellH,
+                        mainAxisSpacing: gap,
+                        crossAxisSpacing: gap,
+                      ),
+                      itemCount: page.items.length,
+                      itemBuilder: (ctx, i) {
+                        final album = page.items[i];
+                        return AlbumCard(
+                          album: album,
+                          width: cellW,
+                          titleMaxLines: 2,
+                          onTap: () => ctx.push('/albums/${album.id}',
+                              extra: album),
+                        );
+                      },
+                    );
+                  }),
                 ),
         );
   }
@@ -260,10 +285,14 @@ class _LikedTab extends ConsumerWidget {
               scrollDirection: Axis.horizontal,
               padding: const EdgeInsets.symmetric(horizontal: 8),
               itemCount: ar.items.length,
-              itemBuilder: (ctx, i) => ArtistCard(
-                artist: ar.items[i],
-                onTap: () => ctx.push('/artists/${ar.items[i].id}'),
-              ),
+              itemBuilder: (ctx, i) {
+                final artist = ar.items[i];
+                return ArtistCard(
+                  artist: artist,
+                  onTap: () =>
+                      ctx.push('/artists/${artist.id}', extra: artist),
+                );
+              },
             ),
           ),
         ],
@@ -275,10 +304,14 @@ class _LikedTab extends ConsumerWidget {
               scrollDirection: Axis.horizontal,
               padding: const EdgeInsets.symmetric(horizontal: 8),
               itemCount: al.items.length,
-              itemBuilder: (ctx, i) => AlbumCard(
-                album: al.items[i],
-                onTap: () => ctx.push('/albums/${al.items[i].id}'),
-              ),
+              itemBuilder: (ctx, i) {
+                final album = al.items[i];
+                return AlbumCard(
+                  album: album,
+                  onTap: () =>
+                      ctx.push('/albums/${album.id}', extra: album),
+                );
+              },
             ),
           ),
         ],