layout improvements

src/lib/stores/appState.ts

@@ -9,6 +9,10 @@ export const isAndroid = writable(false);
 // Shuffle/repeat/next/previous state now lives in the event-driven queue store
 // ($lib/stores/queue), the single source of truth.
 export const showSleepTimerModal = writable(false);
+// Measured height (px) of the fixed bottom UI on Android: BottomNav stacked with
+// the global mini player. Published by the root layout via ResizeObserver so the
+// library list can reserve exactly that much bottom padding (no magic rem guesses).
+export const bottomUiHeight = writable(0);
 
 // Library-specific state
 export const librarySearchQuery = writable("");