fix(downloads): a converted upload too big says so, and a suspended owner's waiting rebuild is not "preparing"

- A converted upload over the space left (not zero) fails with CONVERTED_TOO_BIG_MESSAGE, not
  "storage is full"; it classifies as quota_exceeded by the phrase it shares with the clip's.
- The public watch page says "preparing" only for a job a worker will take: a suspended owner's
  queued job waits for as long as the suspension lasts, so the link says the video is gone, as
  for a paused rebuild.
- The worker's claim docstring names the restart case: a running job put back in the queue waits.

backend/app/worker.py

@@ -167,7 +167,8 @@ def _claim_job() -> int | None:
 
     A suspended user's queued jobs are left where they are: suspension blocks their downloads (not
     only their sign-in), and lifting it lets them run in their old place. A job already running
-    when the user is suspended finishes."""
+    when the user is suspended finishes on that worker; one a worker restart puts back in the queue
+    (`_requeue_if_running`, `_recover_orphans`) waits with the rest."""
     with SessionLocal() as db:
         default_mc = sysconfig.get_int(db, "download_default_max_concurrent")
         rows = db.execute(