fix(downloads,playback): re-encode undecodable audio and carry the media source through

Work from a parallel session in the same working tree, committed here so the
branch is not left half-written. Attribution note: authored in a concurrent
Claude session, not by the author of the preceding commit.

- DR-171: a downloaded video keeps audio the device can actually decode.
  `original` quality asked for a straight copy, so an E-AC-3/AC-3/DTS/TrueHD
  track came down untouched and the webview had nothing to play it with.
- `get_video_download_url` gains the media source, so the URL is built against
  the source actually chosen rather than the item's default.
- Device profile and repository plumbing updated to match.

Verified green as a whole: 656 Rust tests, 945 frontend tests, svelte-check clean.

src/lib/api/bindings.ts

@@ -870,13 +870,32 @@ async getDownloads(userId: string, statusFilter: string[] | null) : Promise<Down
     return await TAURI_INVOKE("get_downloads", { userId, statusFilter });
 },
 /**
- * Pause a download
+ * Pause a download.
+ * 
+ * Writing `status = 'paused'` is only half of it, and used to be all of it: the
+ * streaming task knew nothing about the row and kept running, then overwrote it
+ * with `completed`/`failed` when it finished. The row flicked to "paused" and
+ * undid itself — the reported "pause does not work". Signalling the worker is
+ * what actually stops the bytes; it leaves the `.part` file in place so
+ * [`resume_download`] can continue from it.
+ * 
+ * A queued (not yet started) download has no worker to signal, and the status
+ * write alone is enough — the pump skips anything that is not `pending`.
+ * 
+ * TRACES: UR-055 | DR-168
  */
 async pauseDownload(downloadId: number) : Promise<null> {
     return await TAURI_INVOKE("pause_download", { downloadId });
 },
 /**
- * Resume a paused download
+ * Resume a paused download.
+ * 
+ * Flipping the row back to `pending` is likewise not enough on its own: the
+ * pump is not a poller, it runs when something calls it, so a resumed download
+ * sat untouched until some unrelated event happened to pump the queue. That is
+ * the other half of "resume does not work".
+ * 
+ * TRACES: UR-055 | DR-168
  */
 async resumeDownload(downloadId: number) : Promise<null> {
     return await TAURI_INVOKE("resume_download", { downloadId });