fix(flutter): keep artist avatars round in the Library grid

ArtistCard hardcoded its avatar at Container(width: 124, height:
124) inside a ClipOval. In the Library Artists 3-column grid the
cell is narrower than the card's nominal 140dp width — on a typical
phone the cell is ~109dp, the padded inner content area ~93dp. The
parent constrained the Container's width to ~93dp but the explicit
height stayed 124dp, so ClipOval clipped a 93×124 rectangle and
the avatar rendered as a vertical ellipse.

Fix mirrors AlbumCard's pattern: ArtistCard takes an optional
`width` parameter (default 140 for horizontal carousels) and
derives coverSize = width - 16, so the Container is always square.
ArtistsTab now uses LayoutBuilder to compute cell width and passes
it through, same as AlbumsTab. Avatar stays a true circle at any
cell width.

mainAxisExtent on the grid replaces the previous fixed
childAspectRatio so cell height tracks cellW + name line, with
slack matching AlbumsTab's overflow guard.

flutter_client/lib/library/library_screen.dart

@@ -398,36 +398,52 @@ class _ArtistsTab extends ConsumerWidget {
                   // Listen for scroll-near-bottom and ask the notifier
                   // to fetch the next page. 800px lookahead so the next
                   // page lands before the user reaches the visible end.
-                  child: NotificationListener<ScrollNotification>(
-                    onNotification: (n) {
-                      if (n.metrics.pixels >=
-                          n.metrics.maxScrollExtent - 800) {
-                        ref
-                            .read(_libraryArtistsProvider.notifier)
-                            .loadMore();
-                      }
-                      return false;
-                    },
-                    child: GridView.builder(
-                      padding: const EdgeInsets.all(8),
-                      gridDelegate:
-                          const SliverGridDelegateWithFixedCrossAxisCount(
-                        crossAxisCount: 3,
-                        mainAxisSpacing: 8,
-                        crossAxisSpacing: 8,
-                        childAspectRatio: 0.78,
-                      ),
-                      itemCount: page.items.length,
-                      itemBuilder: (ctx, i) {
-                        final artist = page.items[i];
-                        return ArtistCard(
-                          artist: artist,
-                          onTap: () => ctx.push('/artists/${artist.id}',
-                              extra: artist),
-                        );
+                  // LayoutBuilder + cell-aware ArtistCard width mirrors
+                  // the AlbumsTab pattern so the circular avatar stays
+                  // a true circle on narrow grid cells.
+                  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;
+                    // avatar (cellW - 16) + gap (8) + 1 line name (~18)
+                    // + slack matched to AlbumsTab's overflow guard.
+                    final cellH = (cellW - 16) + 8 + 18 + 8;
+                    return NotificationListener<ScrollNotification>(
+                      onNotification: (n) {
+                        if (n.metrics.pixels >=
+                            n.metrics.maxScrollExtent - 800) {
+                          ref
+                              .read(_libraryArtistsProvider.notifier)
+                              .loadMore();
+                        }
+                        return false;
                       },
-                    ),
-                  ),
+                      child: 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 artist = page.items[i];
+                          return ArtistCard(
+                            artist: artist,
+                            width: cellW,
+                            onTap: () => ctx.push('/artists/${artist.id}',
+                                extra: artist),
+                          );
+                        },
+                      ),
+                    );
+                  }),
                 );
           },
         );

flutter_client/lib/library/widgets/artist_card.dart

@@ -12,15 +12,27 @@ import '../library_providers.dart';
 import 'play_circle_button.dart';
 
 class ArtistCard extends ConsumerWidget {
-  const ArtistCard({required this.artist, required this.onTap, super.key});
+  const ArtistCard({
+    required this.artist,
+    required this.onTap,
+    this.width = 140,
+    super.key,
+  });
   final ArtistRef artist;
   final VoidCallback onTap;
 
+  /// Outer width of the card. Avatar is a circle of width-16 (8dp
+  /// horizontal padding either side). Default suits horizontal lists;
+  /// grids should pass the cell width so the avatar shrinks
+  /// proportionally and stays a true circle.
+  final double width;
+
   @override
   Widget build(BuildContext context, WidgetRef ref) {
     final fs = Theme.of(context).extension<FabledSwordTheme>()!;
+    final coverSize = width - 16;
     return SizedBox(
-      width: 140,
+      width: width,
       child: Material(
         color: Colors.transparent,
         child: InkWell(
@@ -29,15 +41,20 @@ class ArtistCard extends ConsumerWidget {
             padding: const EdgeInsets.symmetric(horizontal: 8),
             child: Column(crossAxisAlignment: CrossAxisAlignment.start, children: [
               // Stack: circular avatar + overlaid play button at bottom-right.
-              // The avatar is a circle (ClipOval) — bottom-right of its
-              // bounding box still places the button inside the visible area
-              // because the button is small relative to the radius.
+              // Avatar size derives from the [width] parameter so the
+              // Library Artists 3-column grid can pass its cell width
+              // (~109dp on typical phones) and the avatar stays a
+              // perfect circle. Previous hardcoded 124×124 got squeezed
+              // horizontally in the grid (cell narrower than 124+16
+              // padding) but kept its 124dp height — ClipOval produced
+              // a visible vertical ellipse. Mirrors AlbumCard's width-
+              // parameter convention.
               Stack(
                 children: [
                   ClipOval(
                     child: Container(
-                      width: 124,
-                      height: 124,
+                      width: coverSize,
+                      height: coverSize,
                       color: fs.slate,
                       child: artist.coverUrl.isEmpty
                           ? SvgPicture.asset('assets/svg/album-fallback.svg',