fix(mobile): remount Favorites lists on numColumns change (GOON-11)

The new Scenes tab uses a 2-column FlatList while Performers/Studios/Movies are
1-column. Switching tabs reused the same FlatList instance, so numColumns changed on
the fly and RN threw "Changing numColumns on the fly is not supported" (5 users).
Give the Scenes list a distinct key ("fav-scenes") from the shared single-column key
("fav-list") so React remounts a fresh FlatList across the 1<->2 boundary.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

mobile/src/screens/FavoritesScreen.tsx

@@ -181,6 +181,9 @@ export function FavoritesScreen() {
 
       {tab === 'scenes' ? (
         <FlatList
+          // key per tab: scenes używa numColumns=2, reszta 1 — bez remountu RN rzuca
+          // "Changing numColumns on the fly is not supported" (GOON-11).
+          key="fav-scenes"
           data={scenesQuery.data?.items ?? []}
           keyExtractor={(s) => s.id}
           numColumns={2}
@@ -220,6 +223,7 @@ export function FavoritesScreen() {
         />
       ) : tab === 'movies' ? (
         <FlatList
+          key="fav-list"
           data={moviesQuery.data?.items ?? []}
           keyExtractor={(f) => f.movie_id}
           renderItem={({ item }) => (
@@ -258,6 +262,7 @@ export function FavoritesScreen() {
         />
       ) : tab === 'performers' ? (
         <FlatList
+          key="fav-list"
           data={performersQuery.data?.items ?? []}
           keyExtractor={(f) => f.performer_id}
           renderItem={({ item }) => (
@@ -303,6 +308,7 @@ export function FavoritesScreen() {
         />
       ) : (
         <FlatList
+          key="fav-list"
           data={studiosQuery.data?.items ?? []}
           keyExtractor={(f) => f.studio_id}
           renderItem={({ item }) => (