feat: qbz-1 streaming, gapless prefetch, accurate scrobbling, Range-seek

Port proven playback architecture from qbqt fork:
- Bounded VecDeque buffer with condvar backpressure (4MB cap)
- decrypt_and_extract_frames for clean FLAC frame extraction from ISOBMFF
- Cancel+restart seeking with sub-segment sample skipping
- start_prefetch / QueueNext for gapless transitions with pre-started downloads
- track_transitioned signaling for scrobbler during gapless playback
- Range-request HTTP seeking for non-segmented (MP3) tracks
- OnceLock HTTP client singleton with cancel-aware chunked downloads
- Accumulated listening time scrobbling (prevents false scrobbles from seeking)
- Array-format Last.fm scrobble params (artist[0], track[0], etc.)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

rust/src/api/models.rs

@@ -74,12 +74,16 @@ pub struct AudioInfoDto {
 #[derive(Debug, Deserialize, Clone, Serialize)]
 pub struct TrackFileUrlDto {
     pub track_id: Option<i64>,
-    pub duration: Option<i64>,
+    pub duration: Option<f64>,
     pub url: Option<String>,
+    pub url_template: Option<String>,
+    pub n_segments: Option<u32>,
     pub format_id: Option<i32>,
     pub mime_type: Option<String>,
     pub sampling_rate: Option<f64>,
     pub bit_depth: Option<i32>,
+    /// qbz-1 encryption key: "qbz-1.<base64url_aes_key>.<base64url_iv>"
+    pub key: Option<String>,
 }
 
 // --- Album ---
@@ -219,6 +223,15 @@ pub struct FavArtistDto {
     pub image: Option<ImageDto>,
 }
 
+// --- Favorite IDs ---
+
+#[derive(Debug, Deserialize, Serialize)]
+pub struct FavIdsDto {
+    pub tracks: Option<Vec<i64>>,
+    pub albums: Option<Vec<String>>,
+    pub artists: Option<Vec<i64>>,
+}
+
 // --- Format ---
 
 #[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize)]