fix(downloads): Retry and Re-download take a cookie added after the failure

The login-wall copy tells the user to add their cookies and press Retry, but
Retry kept the job on the shared asset the worker never attaches a cookie to,
so it failed on the same wall. Resume now moves a pending/errored job onto the
asset enqueue would pick with the cookie (never off a file or a download in
flight).

Re-download salted its fresh asset with the job's previous asset id, which the
cookie gate cannot recompute, so even a cookie download rebuilt without the
cookie. The rebuild salt is now the new asset's own id (plus the user's cookie
salt when one applies), and is_authed_asset recognises it.

backend/app/worker.py

@@ -410,7 +410,7 @@ def _process_job(job_id: int) -> None:
                 asset_error,
                 url=url,
                 cookie_attached=credentials.is_authed_asset(
-                    asset.format_sig, formats.normalize(job.profile_snapshot), job.user_id, url
+                    asset, formats.normalize(job.profile_snapshot), job.user_id, url
                 ),
             )