fix: add missing CSS import and fix UI issues

- Add app.css import to +layout.svelte (fixes broken/light UI)
- Add logging for audio debugging
- Add image fallbacks for album and track artwork
- Fix sidebar/main-content layout (flex-shrink, min-width)
- Remove placeholder data from HomeView
- Add LoginView and SearchView components
- Update window title and branding to QBZ

src-tauri/src/commands/playback.rs

@@ -0,0 +1,62 @@
+//! Playback-related Tauri commands
+
+use tauri::State;
+
+use crate::api::models::Quality;
+use crate::player::PlaybackState;
+use crate::AppState;
+
+/// Play a track by ID
+#[tauri::command]
+pub async fn play_track(track_id: u64, state: State<'_, AppState>) -> Result<(), String> {
+    log::info!("Command: play_track {}", track_id);
+
+    let client = state.client.lock().await;
+
+    // Default to Hi-Res quality, will fallback if not available
+    state
+        .player
+        .play_track(&client, track_id, Quality::HiRes)
+        .await
+}
+
+/// Pause playback
+#[tauri::command]
+pub fn pause_playback(state: State<'_, AppState>) -> Result<(), String> {
+    log::info!("Command: pause_playback");
+    state.player.pause()
+}
+
+/// Resume playback
+#[tauri::command]
+pub fn resume_playback(state: State<'_, AppState>) -> Result<(), String> {
+    log::info!("Command: resume_playback");
+    state.player.resume()
+}
+
+/// Stop playback
+#[tauri::command]
+pub fn stop_playback(state: State<'_, AppState>) -> Result<(), String> {
+    log::info!("Command: stop_playback");
+    state.player.stop()
+}
+
+/// Set volume (0.0 - 1.0)
+#[tauri::command]
+pub fn set_volume(volume: f32, state: State<'_, AppState>) -> Result<(), String> {
+    log::info!("Command: set_volume {}", volume);
+    state.player.set_volume(volume)
+}
+
+/// Seek to position in seconds
+#[tauri::command]
+pub fn seek(position: u64, state: State<'_, AppState>) -> Result<(), String> {
+    log::info!("Command: seek {}", position);
+    state.player.seek(position)
+}
+
+/// Get current playback state
+#[tauri::command]
+pub fn get_playback_state(state: State<'_, AppState>) -> Result<PlaybackState, String> {
+    state.player.get_state()
+}