feat(offline): play downloaded video, and drain the offline sync queue (0.4.6)

Bundles this session's work plus the concurrent search/offline/player changes.
Every gate passes on the combined tree: 885 frontend tests, 610 Rust tests,
clippy clean, boundary clean, trace coverage 86%.

Offline video playback — four separate defects, each of which alone stopped it:

  DR-133  A completed download's file_path is already absolute (the worker
          rewrites it on completion), but the player rooted it a second time and
          handed the webview /data/user/0/app//data/user/0/app/videos/x.mp4.
  DR-134  The asset protocol was never enabled: no protocol-asset feature and no
          assetProtocol config, so convertFileSrc produced URLs nothing answered.
          Also silently defeated the cached-thumbnail path, which fails soft to
          the server copy and hid it whenever the server was reachable.
  DR-137  Tauri's asset protocol answers a range-less request by reading the
          whole file into memory, and only advertises Accept-Ranges from inside
          its range branch, so the first request never learns ranges exist.
          Chromium gave up with PIPELINE_ERROR_READ after ~31s. Local media is
          now served by a loopback HTTP server: bounded 4 MiB chunks streamed
          from the file handle, every response length-delimited, and a range-less
          request answered with one chunk rather than the file. Confined by a
          per-session token and to the app data directory, because loopback is
          shared between apps on Android.
  DR-138  Release builds set usesCleartextTraffic=false, so Android rejected the
          request to that server before any I/O. A network-security-config
          exempts 127.0.0.1 only; a remote server must still be HTTPS.

Downloads:

  DR-135  download_item never records media_type and the reconnect resolver read
          that NULL as 'audio', so a movie queued from a media card had its URL
          resolved by get_audio_stream_url and completed as an audio-only
          transcode. The item's own type now decides.
  DR-136  Rows already downloaded that way are requeued on reconnect, since
          prevention alone leaves them reading "downloaded" and still unplayable.

Known limitation: a download taken at `original` quality is a byte copy of the
source, so it can be any container. One such file is an AVI holding XVID, which
the webview cannot play in any case — the media server serves it correctly and
Chromium refuses it. That needs either a transcoded download preset or the
native ExoPlayer surface work, and is not addressed here.

Also fixes two ID collisions between concurrent work: DR-143 defined twice
(search vs offline gate) and UT-131 defined twice (Episode Focus hero vs channel
cap). The search requirement is now DR-147 and the channel-cap test UT-141, with
their code references and matrix rows updated.

src-tauri/src/lib.rs

@@ -5,6 +5,7 @@ mod credentials;
 mod domain;
 mod download;
 mod jellyfin;
+mod media_server;
 mod playback_mode;
 mod playback_reporting;
 mod player;
@@ -85,6 +86,7 @@ use commands::{
     lms_unsync_player,
     mark_download_completed,
     mark_download_failed,
+    media_local_url,
     offline_get_items,
     offline_is_available,
     offline_search,
@@ -273,6 +275,7 @@ use commands::{
     sync_mark_completed,
     sync_mark_failed,
     sync_mark_processing,
+    sync_process_pending,
     // Sync queue commands
     sync_queue_mutation,
     thumbnail_clear_cache,
@@ -806,6 +809,7 @@ fn specta_builder() -> Builder<tauri::Wry> {
             get_download_storage_stats,
             mark_download_completed,
             mark_download_failed,
+            media_local_url,
             start_download,
             enqueue_download,
             enqueue_video_downloads,
@@ -846,6 +850,7 @@ fn specta_builder() -> Builder<tauri::Wry> {
             sync_mark_completed,
             sync_mark_failed,
             sync_get_pending_count,
+            sync_process_pending,
             sync_cleanup_completed,
             sync_clear_user,
             // Thumbnail cache and image commands
@@ -1238,6 +1243,22 @@ pub fn run() {
             let smart_cache_wrapper = SmartCacheWrapper(Mutex::new(smart_cache));
             app.manage(smart_cache_wrapper);
 
+            // Serve downloaded media over loopback HTTP. The webview cannot
+            // stream a large file through the asset protocol (see media_server),
+            // so local playback resolves its URL from here instead.
+            // TRACES: UR-071 | DR-137
+            info!("[INIT] Starting local media server...");
+            let media_server = match media_server::start(app_data_dir.clone()) {
+                Ok(s) => Some(s),
+                Err(e) => {
+                    // Not fatal: streaming still works, and the command reports
+                    // a clear error if local playback is attempted.
+                    error!("[INIT ERROR] Local media server failed to start: {}", e);
+                    None
+                }
+            };
+            app.manage(media_server::MediaServerWrapper(media_server));
+
             // Initialize download manager
             info!("[INIT] Initializing download manager...");
             let download_dir = app_data_dir.join("downloads");
@@ -1319,6 +1340,13 @@ pub fn run() {
             info!("[INIT] Starting favourites drain...");
             commands::favorites::spawn_favorites_drain(app.handle().clone());
 
+            // Push playback reports queued while the server was unreachable.
+            // Without this the `sync_queue` rows the reporter writes offline
+            // are never sent and the offline banner's count only grows.
+            // TRACES: UR-025, UR-002 | DR-131
+            info!("[INIT] Starting sync-queue drain...");
+            commands::sync_drain::spawn_sync_queue_drain(app.handle().clone());
+
             info!("[INIT] Application setup completed successfully");
             Ok(())
         })