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-tauri/src/commands/repository.rs

@@ -804,7 +804,7 @@ pub fn repository_get_subtitle_url(
 #[tauri::command]
 #[specta::specta]
 #[allow(dead_code)]
-pub fn repository_get_video_download_url(
+pub async fn repository_get_video_download_url(
     manager: State<'_, RepositoryManagerWrapper>,
     handle: String,
     item_id: String,
@@ -812,9 +812,16 @@ pub fn repository_get_video_download_url(
     media_source_id: Option<String>,
 ) -> Result<String, String> {
     let repo = manager.0.get(&handle).ok_or("Repository not found")?;
-    Ok(repo
-        .as_ref()
-        .get_video_download_url(&item_id, &quality, media_source_id.as_deref()))
+    // Async because the audio-codec policy has to know what the source's audio
+    // is before it can decide whether the file may be copied verbatim (DR-171).
+    // The frontend calls this exactly as before — the decision stays in Rust.
+    Ok(crate::repository::resolve_video_download_url(
+        repo.as_ref(),
+        &item_id,
+        &quality,
+        media_source_id.as_deref(),
+    )
+    .await)
 }
 
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