Set a CSP with script-src 'self' (Tauri nonces the one inline bootstrap script),
object-src/frame-src 'none', and necessarily-permissive img/media/connect for the
user-supplied Jellyfin origin. Narrow assetProtocol $APPDATA/** -> thumbnails/**,
which is convertFileSrc's only remaining caller.
Conflict resolution: scripts/extract-traces.test.ts pinned counts summed rather
than side-picked — DR-189 and DR-198 were added independently on two branches,
so DR 187 -> 189 and total 330 -> 332. docs/traceability.md regenerated.
