feat(queue): show playback source in tech strip with preload tracking

Add source badges for offline, cache, and stream playback in the queue tech line, including localized tooltips across shipped locales.

Track Rust preload-ready events by stream track id and latch the selected source per track, with dev logs to debug preload/source mismatches during next-track handoff.

src-tauri/src/audio.rs

@@ -3076,11 +3076,13 @@ pub fn audio_set_eq(gains: [f32; 10], enabled: bool, pre_gain: f32, state: State
 pub async fn audio_preload(
     url: String,
     duration_hint: f64,
+    app: AppHandle,
     state: State<'_, AudioEngine>,
 ) -> Result<(), String> {
     {
         let preloaded = state.preloaded.lock().unwrap();
         if preloaded.as_ref().is_some_and(|p| same_playback_target(&p.url, &url)) {
+            let _ = app.emit("audio:preload-ready", url.clone());
             return Ok(());
         }
     }
@@ -3102,7 +3104,9 @@ pub async fn audio_preload(
         response.bytes().await.map_err(|e| e.to_string())?.into()
     };
     let _ = duration_hint; // kept in API for compatibility
+    let url_for_emit = url.clone();
     *state.preloaded.lock().unwrap() = Some(PreloadedTrack { url, data });
+    let _ = app.emit("audio:preload-ready", url_for_emit);
     Ok(())
 }