fix(e12): close what round one broke, and revert two fixes that overreached

Round two of the review loop, on round one's own diff. Two of its findings were
regressions the fixes themselves introduced, which is exactly what the loop is for:

**A per-user refusal was writing onto a shared row.** MediaAssets are deduped across
users, and the generic failure handler puts the message on the asset — right for an
upstream failure, wrong for "your storage is full". Two users queuing the same video share
one asset, so the first user hitting their cap failed the second user's job with the first
one's private reason, telling someone with an empty library to free up space. The refusal
now raises `_OwnerRefused`, caught separately: the job fails, the asset goes back to
`pending` for whoever else holds it. Pinned by a test that drives `_download` directly —
the refusal happens before extraction, so nothing needs stubbing.

**The restore scripts restarted the app, undoing the restore.** `docker compose start`
re-runs the container command, and that runs `alembic upgrade head` — so on the rollback
path this documents as recommended (restore the dump, THEN pin the older tag) the newer
image immediately re-applied the migrations the restore had just undone, and on a FAILED
restore it put the app back on a half-restored schema. Both are the opposite of why the
stop was added. Nothing is restarted automatically now; the scripts say what to run and
when, and the docs' snippets say the same.

**Reverted rather than patched:** the OnboardingWizard toast (the wizard already renders
that failure inline, next to a Retry button — three recoveries for one failure), and
`useVerifyEntry`'s "each new link clears the other". The latter blanked the signed-out
card's only banner, where nothing renders the reset flag to replace it. The two states are
independent again; what changes is that `dismiss` peels ONE layer, which is what the
original finding was actually about.

Also: `Stats` uses the YouTube helper rather than the bare one, so the route's English 403
detail no longer beats the translated fallback under a Hungarian UI; `urlparse` guarded
alongside `.port` (an unclosed bracket raised just as late), the reason renamed `malformed`
since "bad port" misdescribes it; three docstrings narrowed to what the code actually does
(the worker's byte check is per-job, not an aggregate ledger, and not on the edit path;
the redirect residual leaks a reachability oracle, which the note had denied; the
invalidation helper does not cover suspend); the pasted Windows recipe wrapped so `throw`
can stop it; the bash one-liner's failure branch no longer exits 0; and the tests that were
missing for the round-one fixes — the account panel's error paths, the invalidation set,
and the shared-asset case above.

Gate green: vitest 685, pytest 950.

backend/app/downloads/quota.py

@@ -6,9 +6,14 @@ Limits come from a per-user DownloadQuota row if the admin set one, else the sys
 `unlimited` (e.g. the admin's own account) bypasses the byte cap.
 
 Enforcement split: max_jobs + max_bytes are checked at enqueue (they bound holdings); per-user
-max_concurrent is enforced by the worker at claim time (it bounds simultaneous downloads). max_bytes
-is checked a SECOND time in the worker, via `remaining_bytes` — enqueue can only compare the
-footprint as it stood when the job was created, and earlier jobs may have filled the cap since.
+max_concurrent is enforced by the worker at claim time (it bounds simultaneous downloads).
+
+DOWNLOAD jobs additionally consult `remaining_bytes` in the worker, because enqueue can only compare
+the footprint as it stood when the job was created and earlier jobs may have filled the cap since.
+That is a per-job ceiling, not an aggregate ledger: concurrent jobs of one user each read the same
+remainder (in-flight bytes are not `ready`, so `footprint` cannot see them), so a wave of
+max_concurrent downloads can still land over the cap — the deliberate trade, since a download's size
+is unknown until it finishes. Edit jobs do not consult it at all (tracked as SEC-19).
 """
 
 from dataclasses import dataclass