address the review of the tap targets

The "stays inert" test was tautological: the render helper always passed non-null no-op
lambdas, so its assertion held for any implementation. It now passes nullable callbacks
and asserts the targets are disabled, which fails if the gate is removed.

Accessibility: both taps carry onClickLabel ("Open album"/"Open artist") and the artist
box spans the full row, and the now playing cover passes showPlaceholder = coverArt ==
null so the always-present placeholder letter is not merged into the tap target's label
(the same flash the artist detail cells had).

Left as-is: the artist target is still one line tall (~20dp), and the album detail
subtitle tap covers the year too. Both are layout/scope trade-offs.

app/src/main/kotlin/com/subtracks/ui/playback/NowPlayingScreen.kt

@@ -260,7 +260,10 @@ fun NowPlayingScreen(
                                     .weight(1f)
                                     .fillMaxWidth()
                                     .padding(top = 2.dp)
-                                    .clickable(enabled = onAlbumClick != null) { onAlbumClick?.invoke() }
+                                    .clickable(
+                                        enabled = onAlbumClick != null,
+                                        onClickLabel = "Open album",
+                                    ) { onAlbumClick?.invoke() }
                                     .testTag(NOW_PLAYING_COVER_TAG),
                             contentAlignment = Alignment.Center,
                         ) {
@@ -268,6 +271,7 @@ fun NowPlayingScreen(
                                 ref = coverArt,
                                 name = state.item?.title.orEmpty(),
                                 thumbnailRef = thumbnailRef,
+                                showPlaceholder = coverArt == null,
                                 square = false,
                                 elevation = 3.dp,
                                 modifier = Modifier.fillMaxSize(),
@@ -303,8 +307,12 @@ fun NowPlayingScreen(
                             Box(
                                 modifier =
                                     Modifier
+                                        .fillMaxWidth()
                                         .height(subtitleHeight)
-                                        .clickable(enabled = onArtistClick != null) { onArtistClick?.invoke() },
+                                        .clickable(
+                                            enabled = onArtistClick != null,
+                                            onClickLabel = "Open artist",
+                                        ) { onArtistClick?.invoke() },
                                 contentAlignment = Alignment.Center,
                             ) {
                                 Text(