fix(files): a file is added when it is done, not when it was asked for

A download that failed for days and then went through sat days down the library, under its
request date, and read as missing. A job now records when it became done (`ready_at`), stamped
where the expiry already is (`folders.stamp_done`, `finalize_if_running`) and on an insert that is
already done; a check constraint holds every path to done to it. The library sorts and dates its
"Added" by it; the queue keeps the request order.

The migration dates a file from before by its "ready to watch" notice where the inbox still holds
one, else by its request date, where it already sat.

backend/tests/test_upload_conversion.py

@@ -407,7 +407,7 @@ def test_the_sweep_keeps_an_aged_upload_file_its_row_names_in_any_state(
     _probe(monkeypatch)
     job, asset = _ingest(db, _root, make_user().id)
     path = storage.abs_path(str(_root), asset.rel_path)
-    job.status, asset.status = job_status, asset_status
+    job.status, asset.status, job.ready_at = job_status, asset_status, job.created_at
     db.commit()
     _aged(path)
 
@@ -427,7 +427,11 @@ def _route_moved(db, job, asset, job_status: str, ref_count: int) -> None:
     """What the cancel/pause/delete route leaves behind, written as SQL: the session's copy of
     `ref_count` is stale (the routes count it in SQL), so an ORM assignment of the same value would
     write nothing."""
-    db.execute(update(DownloadJob).where(DownloadJob.id == job.id).values(status=job_status))
+    db.execute(
+        update(DownloadJob)
+        .where(DownloadJob.id == job.id)
+        .values(status=job_status, ready_at=DownloadJob.created_at)
+    )
     db.execute(update(MediaAsset).where(MediaAsset.id == asset.id).values(ref_count=ref_count))
     db.commit()
 
@@ -609,6 +613,7 @@ def test_the_admin_storage_view_names_each_users_quota_and_files(
     done, _ = _ingest(db, _root, u.id, size=10)
     waiting, _ = _ingest(db, _root, u.id, name="b.mov", size=5)
     done.status, waiting.status = "done", "queued"
+    done.ready_at = done.created_at
     db.commit()
     admin = as_user(make_user(role="admin"))
     put = admin.put(f"/api/admin/downloads/quota/{u.id}", json={"max_bytes": 1000})