fix(reader): the Takeout import holds up under abuse, races and a run it cannot see

- Uploads: one at a time per user and ten an hour, each refused only after its body arrived;
  the history read an entry at a time (32 MiB cap), a Watch later list capped at YouTube's 5000,
  a user's kept videos at 200k; any unreadable shape is a 422, not a 500.
- Quota: Watch later lookups stop at the backfill reserve and at a per-user daily share; what is
  not asked about waits, known videos still go in, and the shorts job retries the rest.
- Staging and settling share one per-user advisory lock (no deadlock); a run settles only the
  rows it read, so a row staged meanwhile is never called gone.
- A failed run's notice names a translated failure, never the upstream's text.
- The status says when an import is queued; the page watches it to its end even when left, then
  reads the feed, its counts and the playlists again.
- Settings: one live region, the zone kept (unavailable) while a run goes, focus handed back,
  a missed drop kept from the browser, an oversize file refused before it is sent.
- Scheduler and run lists show Takeout runs by the importing user.

scripts/e2e_seed.py

@@ -181,6 +181,28 @@ def _seed_account(db, email: str, role: str, display_name: str) -> dict:
             saved = svid.id
     db.commit()
 
+    # 5. Videos the Takeout import marks watched: from the subscribed channels, and already cleared by
+    #    the Shorts probe — one not yet probed would wait for it, and the import spec would count
+    #    nothing. One per browser project: they share this account, and a video imported once is not
+    #    marked again.
+    known = (
+        list(
+            db.scalars(
+                select(Video.id)
+                .where(
+                    Video.channel_id.in_(channel_ids),
+                    Video.shorts_probed.is_(True),
+                    Video.is_short.is_(False),
+                    Video.id.not_in(used | {saved} if saved else used),
+                )
+                .order_by(Video.published_at.desc())
+                .limit(5)
+            )
+        )
+        if channel_ids
+        else []
+    )
+
     return {
         "user_id": user.id,
         "email": email,
@@ -188,6 +210,7 @@ def _seed_account(db, email: str, role: str, display_name: str) -> dict:
         "in_progress": in_progress,
         "watched": watched,
         "saved": saved,
+        "takeout_known": known,
     }