feat(android): swap top-nav Library icon to Lucide.SquareLibrary

LibraryBig (stacked book spines) didn't read as "Library" without
the label — easy to misread as a generic stack/columns icon.
SquareLibrary frames the same books-on-shelf glyph inside a
rounded square, matching the visual weight of the neighbouring
House and Search icons better and reading more clearly as a
distinct tappable destination.

Untouched: the RequestsScreen per-row "album"-kind avatar still
uses LibraryBig (parity with Flutter's lib/requests/requests_screen.dart).

android/app/src/main/java/com/fabledsword/minstrel/shared/widgets/MainAppBarActions.kt

@@ -15,8 +15,8 @@ import androidx.hilt.navigation.compose.hiltViewModel
 import androidx.lifecycle.compose.collectAsStateWithLifecycle
 import androidx.navigation.NavHostController
 import com.composables.icons.lucide.House
-import com.composables.icons.lucide.LibraryBig
 import com.composables.icons.lucide.Lucide
+import com.composables.icons.lucide.SquareLibrary
 import com.composables.icons.lucide.EllipsisVertical
 import com.composables.icons.lucide.Search as SearchIcon
 import com.fabledsword.minstrel.nav.Admin
@@ -58,7 +58,7 @@ fun MainAppBarActions(
         }
         if (currentRouteName != Library::class.qualifiedName) {
             IconButton(onClick = { navController.navigate(Library) }) {
-                Icon(Lucide.LibraryBig, contentDescription = "Library")
+                Icon(Lucide.SquareLibrary, contentDescription = "Library")
             }
         }
         if (currentRouteName != SearchRoute::class.qualifiedName) {