feat(web/player): self-heal a stale system-playlist / radio queue on total failure

When the whole queue proves unplayable (e.g. a tab left open across the
daily system-playlist rebuild — the exact stale-snapshot case), the player
now re-pulls the fresh snapshot and resumes instead of dead-ending on
"Try again". The seeder hands the store an opaque refetch closure so the
store stays decoupled from the playlist API and the per-artist
(songs_like_artist) identity problem: single-instance variants re-pull via
systemShuffle, per-artist mixes via getPlaylist(id), radio re-seeds from
its track. Bounded to one self-heal per exhaustion (reset on the next
successful play) so a still-broken refresh can't loop; "Try again" stays
the genuine last resort. Wired from PlaylistCard, the playlist detail page,
and playRadio. Issue #968.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

web/src/lib/components/PlaylistCard.svelte

@@ -5,6 +5,7 @@
   import { user } from '$lib/auth/store.svelte';
   import { getPlaylist, systemShuffle, refreshSystem } from '$lib/api/playlists';
   import { playlistTrackToRef } from '$lib/playlists/playlistTrackToRef';
+  import { systemPlaylistRefetch } from '$lib/playlists/systemRefetch';
   import { errCode } from '$lib/api/errors';
   import { qk } from '$lib/api/queries';
   import { playQueue } from '$lib/player/store.svelte';
@@ -80,7 +81,14 @@
         const detail = await systemShuffle(variant);
         const refs = toTrackRefs(detail.tracks);
         if (refs.length > 0) {
-          playQueue(refs, 0, { source: variant });
+          playQueue(refs, 0, {
+            source: variant,
+            refetch: systemPlaylistRefetch({
+              variant,
+              playlistId: playlist.id,
+              perArtist: false,
+            }),
+          });
         }
       } else {
         const detail = await getPlaylist(playlist.id);
@@ -93,7 +101,14 @@
           // so source attribution stays absent — the PlaylistCard
           // test pins this contract.
           if (variant != null) {
-            playQueue(refs, 0, { source: variant });
+            playQueue(refs, 0, {
+              source: variant,
+              refetch: systemPlaylistRefetch({
+                variant,
+                playlistId: playlist.id,
+                perArtist: true,
+              }),
+            });
           } else {
             playQueue(refs, 0);
           }