feat(discover): Not interested menu action with live removal + backfill

ArtistGridCard's context menu gains a 4th item (Not interested,
thumbs-down icon; popup height bumped for the extra row) that emits
("artist", id, "not-interested") through the existing media-action
chain. The new central arm persists the dismissal to the reco_dismiss
store and, when the artist is in a reco rail, removes the card live and
backfills the freed slot from the rail's retained overflow (already
Qobuz-validated — no network; the pop re-checks live exclusions and
cross-rail visibility). Dismissed from a non-reco surface, the display
name is resolved via get_artist before persisting, so the management
list and toast still read well.

km

crates/qbz-ui/ui/discover/ArtistGridCard.slint

@@ -203,7 +203,7 @@ export component ArtistGridCard inherits Rectangle {
                     x: 21px;
                     y: 143px;
                     width: 196px;
-                    height: 3 * 33px + 10px;
+                    height: 4 * 33px + 10px;
                     ContextMenu {
                         ContextMenuItem {
                             icon: @image-url("../assets/icons/user.svg");
@@ -228,6 +228,15 @@ export component ArtistGridCard inherits Rectangle {
                                 root.media-action(root.follow-kind, root.artist.id, "follow");
                             }
                         }
+                        // Reco-scoped dismissal (NOT the blacklist): the artist
+                        // leaves the Recommendations rails only.
+                        ContextMenuItem {
+                            icon: @image-url("../assets/icons/thumbs-down.svg");
+                            label: @tr("Not interested");
+                            clicked => {
+                                root.media-action("artist", root.artist.id, "not-interested");
+                            }
+                        }
                     }
                 }
             }