fix(flutter): full-player kebab nav + restore artistAlbums SWR

Two unrelated issues, batched.

Full-player kebab → "Go to album/artist" still crashed with
_debugCheckDuplicatedPageKeys despite the prior onBeforeNavigate
fix. Cause: pop() and push() ran in the same frame, so go_router's
page-key reservation table briefly contained both /now-playing AND
the destination shell-child, tripping the duplicate-key assert.

Refactor: replace onBeforeNavigate with onNavigate(path), where the
host receives the path AFTER the sheet pops and owns the
navigation entirely. The full player wires:
  onNavigate: (path) async {
    await Navigator.of(context).maybePop();
    if (context.mounted) GoRouter.of(context).push(path);
  }
Awaiting the pop guarantees /now-playing is fully gone from the
navigator's page list before the push starts.

Mini player + track rows + everywhere else use the default (no
onNavigate) path that does context.push(path) inline — they're
already inside the ShellRoute, no race possible.

Restored alwaysRefresh: true on artistAlbumsProvider. Dropping it
in the cache-loop fix had a side effect: if drift's cachedAlbums
held only a subset of an artist's albums (user previously visited
just one album by them), the artist detail page rendered that
partial list forever — provider only fetched on empty drift, never
on partial drift. The metadata prefetcher only mass-warms
artistProvider (single row), so re-enabling SWR on artistAlbums
won't recreate the storm.

flutter_client/lib/library/library_providers.dart

@@ -101,6 +101,14 @@ final artistAlbumsProvider =
     isOnline: () async => (await ref
         .read(connectivityProvider.future)
         .timeout(const Duration(seconds: 3), onTimeout: () => true)),
+    // SWR: re-fetch the full album list on every visit. Without this,
+    // a previously-incomplete drift cache (e.g. user had only opened
+    // one album by this artist, so cachedAlbums had just that row)
+    // would render forever as a partial list. The prefetcher only
+    // warms artistProvider (single row), so this provider isn't
+    // mass-instantiated and the storm risk that motivated dropping
+    // alwaysRefresh elsewhere doesn't apply here.
+    alwaysRefresh: true,
     tag: 'artistAlbums($artistId)',
   );
 });