Card filter: show only Universes Beyond cards

The Universes Beyond toggle now cycles off → hide → only, backed by a new
only_universes_beyond library filter. Choosing "only" counts as a real
query, so Card Search runs it on its own.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

crates/mtgc-core/src/filters.rs

@@ -53,6 +53,9 @@ fn push_card_filters(
         if filter.exclude_universes_beyond {
             sql.push_str(" AND oc.universes_beyond = 0");
         }
+        if filter.only_universes_beyond {
+            sql.push_str(" AND oc.universes_beyond = 1");
+        }
         if filter.exclude_digital_only {
             sql.push_str(" AND oc.digital_only = 0");
         }
@@ -387,7 +390,7 @@ mod tests {
     }
 
     #[test]
-    fn excluding_universes_beyond_hides_flagged_cards_only_when_asked() {
+    fn universes_beyond_filters_hide_or_keep_only_flagged_cards() {
         let fx = owned_fixture();
         // Stand in for what the ingest derives: a card that exists only as
         // Universes Beyond.
@@ -410,6 +413,16 @@ mod tests {
         // Off unless asked for — this must not quietly change existing searches.
         let all = names(&fx.catalog.search_library(&LibraryFilter::default()).unwrap());
         assert!(all.contains(&"Serra Angel".to_string()));
+
+        let f = LibraryFilter {
+            only_universes_beyond: true,
+            ..Default::default()
+        };
+        assert_eq!(
+            names(&fx.catalog.search_library(&f).unwrap()),
+            vec!["Serra Angel"],
+            "only the flagged card is kept"
+        );
     }
 
     #[test]

crates/mtgc-core/src/model.rs

@@ -421,6 +421,10 @@ pub struct LibraryFilter {
     /// existed, the same way the other reference-schema additions degrade.
     #[serde(default)]
     pub exclude_universes_beyond: bool,
+    /// The opposite: only cards that exist only as Universes Beyond. Inert
+    /// against an older `reference.db` in the same way.
+    #[serde(default)]
+    pub only_universes_beyond: bool,
     /// Hide cards that exist only on Arena/MTGO (Alchemy rebalances and the
     /// like) and so can never be in a physical collection.
     #[serde(default)]