fix: Compose UI 품질 개선 — contentType, derivedStateOf, 색상 토큰, 접근성

app/src/main/java/com/happyseal/zenplayer/core/ui/component/AlbumArtThumbnail.kt

@@ -67,7 +67,7 @@ fun AlbumArtThumbnail(
         ) {
             Icon(
                 imageVector = Icons.Filled.MusicNote,
-                contentDescription = null,
+                contentDescription = "앨범 아트",
                 tint = color.contentColor(),
             )
         }

app/src/main/java/com/happyseal/zenplayer/features/playlist/ui/PlaylistDetailScreen.kt

@@ -144,7 +144,7 @@ fun PlaylistDetailScreen(
                                     modifier = Modifier.padding(bottom = ZenDimension.Spacing.S),
                                 )
                             }
-                            itemsIndexed(state.tracks, key = { _, playlistTrack -> playlistTrack.rowId }) { index, playlistTrack ->
+                            itemsIndexed(state.tracks, key = { _, playlistTrack -> playlistTrack.rowId }, contentType = { _, _ -> "playlistTrack" }) { index, playlistTrack ->
                                 val isActive = miniPlayerUiState.currentTrackTitle == playlistTrack.track.title
                                 PlaylistTrackItem(
                                     playlistTrack = playlistTrack,
@@ -284,13 +284,13 @@ private fun PlaylistTrackItem(
                 Box(
                     modifier = Modifier
                         .matchParentSize()
-                        .background(TealThemeColor.TealPrimary.copy(alpha = 0.4f)),
+                        .background(MaterialTheme.colorScheme.primary.copy(alpha = 0.4f)),
                     contentAlignment = Alignment.Center,
                 ) {
                     Icon(
                         imageVector = Icons.Default.PlayArrow,
                         contentDescription = null,
-                        tint = TealThemeColor.TealOnPrimary,
+                        tint = MaterialTheme.colorScheme.onPrimary,
                         modifier = Modifier.size(ZenDimension.IconSize.S),
                     )
                 }

app/src/main/java/com/happyseal/zenplayer/features/timer/ui/components/ZenPomodoroTimer.kt

@@ -58,6 +58,8 @@ import androidx.compose.ui.graphics.drawscope.drawIntoCanvas
 import androidx.compose.ui.graphics.graphicsLayer
 import androidx.compose.ui.graphics.toArgb
 import androidx.compose.ui.res.stringResource
+import androidx.compose.ui.semantics.contentDescription
+import androidx.compose.ui.semantics.semantics
 import androidx.compose.ui.text.font.FontWeight
 import androidx.compose.ui.tooling.preview.Preview
 import androidx.compose.ui.unit.Dp
@@ -311,7 +313,9 @@ private fun TimerCircleContent(
                 text = pomodoroUiState.remaining.toTimeString(),
                 style = TimerTextStyle.copy(fontSize = 48.sp, fontWeight = FontWeight.Light),
                 color = sessionColor,
-                modifier = Modifier.alpha(blinkAlpha),
+                modifier = Modifier
+                    .alpha(blinkAlpha)
+                    .semantics { contentDescription = "남은 시간 ${pomodoroUiState.remaining.toTimeString()}" },
             )
 
             Spacer(modifier = Modifier.height(8.dp))

app/src/main/java/com/happyseal/zenplayer/zen/miniplayer/ZenPlayerBar.kt

@@ -45,6 +45,7 @@ import androidx.compose.material3.Surface
 import androidx.compose.material3.Text
 import androidx.compose.runtime.Composable
 import androidx.compose.runtime.LaunchedEffect
+import androidx.compose.runtime.derivedStateOf
 import androidx.compose.runtime.getValue
 import androidx.compose.runtime.mutableFloatStateOf
 import androidx.compose.runtime.mutableStateOf
@@ -95,7 +96,7 @@ internal fun ZenPlayerBar(
 
     Surface(
         modifier = modifier.fillMaxWidth(),
-        color = Color.White.copy(alpha = 0.8f),
+        color = MaterialTheme.colorScheme.surface.copy(alpha = 0.8f),
         shape = RoundedCornerShape(topStart = ZenDimension.Corner.Pill, topEnd = ZenDimension.Corner.Pill),
         border = BorderStroke(1.dp, Color.White.copy(alpha = ZenAlpha.DISABLED)),
     ) {
@@ -230,8 +231,11 @@ private fun MusicContent(
 
     Spacer(modifier = Modifier.height(ZenDimension.Spacing.S))
 
-    val playbackProgress =
-        if (duration > 0) (currentPosition.toFloat() / duration).coerceIn(0f, 1f) else 0f
+    val playbackProgress by remember(duration, currentPosition) {
+        derivedStateOf {
+            if (duration > 0) (currentPosition.toFloat() / duration).coerceIn(0f, 1f) else 0f
+        }
+    }
     var sliderPosition by remember { mutableFloatStateOf(playbackProgress) }
     var isDragging by remember { mutableStateOf(false) }
     LaunchedEffect(playbackProgress) {
@@ -417,14 +421,14 @@ private fun PlayPauseButton(
                         imageVector = Icons.Default.Pause,
                         contentDescription = stringResource(R.string.cd_pause),
                         modifier = Modifier.size(ZenDimension.IconSize.L),
-                        tint = Color.White,
+                        tint = MaterialTheme.colorScheme.onPrimary,
                     )
                 } else {
                     Icon(
                         imageVector = Icons.Default.PlayArrow,
                         contentDescription = stringResource(R.string.cd_play),
                         modifier = Modifier.size(ZenDimension.IconSize.L),
-                        tint = Color.White,
+                        tint = MaterialTheme.colorScheme.onPrimary,
                     )
                 }
             }

app/src/main/java/com/happyseal/zenplayer/zen/musicselect/ZenAllTracksTabContent.kt

@@ -43,6 +43,7 @@ import androidx.compose.material3.Surface
 import androidx.compose.material3.Text
 import androidx.compose.material3.TextButton
 import androidx.compose.runtime.Composable
+import androidx.compose.runtime.derivedStateOf
 import androidx.compose.runtime.getValue
 import androidx.compose.runtime.mutableStateOf
 import androidx.compose.runtime.remember
@@ -78,7 +79,7 @@ internal fun AllTracksTabContent(
 ) {
     val context = LocalContext.current
     var selectedTracks by remember { mutableStateOf(setOf<Track>()) }
-    val isSelectionMode = selectedTracks.isNotEmpty()
+    val isSelectionMode by remember { derivedStateOf { selectedTracks.isNotEmpty() } }
     var showPlaylistDialog by remember { mutableStateOf(false) }
 
     Box(modifier = modifier.fillMaxSize()) {
@@ -252,7 +253,7 @@ private fun TrackListContent(
                 ),
                 verticalArrangement = Arrangement.spacedBy(ZenDimension.Spacing.M),
             ) {
-                itemsIndexed(uiState.tracks, key = { _, track -> track.id }) { index, track ->
+                itemsIndexed(uiState.tracks, key = { _, track -> track.id }, contentType = { _, _ -> "track" }) { index, track ->
                     val isSelected = track in selectedTracks
                     TrackItem(
                         track = track,