refactor: retire the images tarball backup

Images and attachments are backed up off-site, one object per file, so the
tar+zstd of /images goes: its service and restore, both tasks, the trigger and
restore routes, the Keep last setting, the screen's Images section, and the
tests. Migration 0122 drops backup_run.tar_path and
import_settings.backup_images_keep_last_n and deletes any images runs.

The local database dump stays for an install with no off-site destination,
and the Backups card now says plainly that images and attachments are backed
up only off-site.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/test_tasks_backup.py

@@ -36,9 +36,6 @@ def fake_subprocess_and_images_root(monkeypatch, tmp_path):
         if "pg_dump" in cmd:
             i = cmd.index("-f")
             Path(cmd[i + 1]).write_bytes(b"-- fake pg_dump\n")
-        elif cmd[0] == "tar" and "-cf" in cmd:
-            i = cmd.index("-cf")
-            Path(cmd[i + 1]).write_bytes(b"fake tar payload")
 
     def _fake_run(cmd, **kwargs):
         _sentinel(cmd)
@@ -55,7 +52,7 @@ def fake_subprocess_and_images_root(monkeypatch, tmp_path):
         def kill(self):
             self.returncode = -9
 
-    # backup_db/backup_images go through _run_bounded (Popen); restore via run.
+    # backup_db goes through _run_bounded (Popen); restore via run.
     monkeypatch.setattr("subprocess.run", _fake_run)
     monkeypatch.setattr("subprocess.Popen", _FakePopen)
 
@@ -67,7 +64,6 @@ def _seed_backup(db_sync, *, kind, status, started_at, tag=None,
         triggered_by="manual", started_at=started_at,
         finished_at=finished_at or (started_at + timedelta(seconds=10)),
         sql_path="/tmp/fake.sql" if kind == "db" else None,
-        tar_path="/tmp/fake.tar.zst" if kind == "images" else None,
         manifest={},
     )
     db_sync.add(row)
@@ -185,22 +181,6 @@ async def test_an_off_site_dump_that_fails_is_recorded_with_why(db_sync, monkeyp
     assert row.error == "DumpFailed: pg_dump: error: connection lost"
 
 
-# --- backup_images_task ---------------------------------------------
-
-
-@pytest.mark.asyncio
-async def test_backup_images_task_creates_backup_run(db_sync):
-    from backend.app.tasks.backup import backup_images_task
-    result = backup_images_task.delay().get()
-    row = db_sync.execute(
-        select(BackupRun.kind, BackupRun.status, BackupRun.tar_path)
-        .where(BackupRun.id == result["backup_run_id"])
-    ).one()
-    assert row.kind == "images"
-    assert row.status == "ok"
-    assert row.tar_path and row.tar_path.endswith(".tar.zst")
-
-
 # --- restore_db_task ------------------------------------------------
 
 
@@ -226,11 +206,11 @@ async def test_restore_db_task_rejects_non_db_source(db_sync):
     from backend.app.tasks.backup import restore_db_task
 
     now = datetime.now(UTC)
-    img_id = _seed_backup(db_sync, kind="images", status="ok", started_at=now)
+    media_id = _seed_backup(db_sync, kind="media", status="ok", started_at=now)
     db_sync.commit()
 
     with pytest.raises(ValueError):
-        restore_db_task.delay(source_backup_run_id=img_id).get()
+        restore_db_task.delay(source_backup_run_id=media_id).get()
 
 
 # --- prune_backups --------------------------------------------------
@@ -243,7 +223,6 @@ def test_prune_backups_keeps_last_n_untagged_per_kind(db_sync):
         select(ImportSettings).where(ImportSettings.id == 1)
     ).scalar_one()
     s.backup_db_keep_last_n = 2
-    s.backup_images_keep_last_n = 1
     db_sync.commit()
 
     now = datetime.now(UTC)
@@ -251,13 +230,13 @@ def test_prune_backups_keeps_last_n_untagged_per_kind(db_sync):
         _seed_backup(db_sync, kind="db", status="ok",
                      started_at=now - timedelta(hours=i))
     for i in range(3):
-        _seed_backup(db_sync, kind="images", status="ok",
+        _seed_backup(db_sync, kind="media", status="ok",
                      started_at=now - timedelta(hours=i))
     db_sync.commit()
 
     result = prune_backups.apply().get()
     assert result["db_deleted"] == 2
-    assert result["images_deleted"] == 2
+    assert result["media_deleted"] == 0        # 60 media runs are kept
 
 
 def test_prune_backups_protects_tagged_rows(db_sync):
@@ -321,9 +300,9 @@ def test_stall_sweep_flips_db_fast_but_spares_running_images(db_sync):
         db_sync, kind="db", status="running",
         started_at=now - timedelta(minutes=50),
     )
-    # An images backup running 50 min is still well under the 7h window → spared.
+    # A test restore running 50 min is still well under the 7h window → spared.
     img_id = _seed_backup(
-        db_sync, kind="images", status="running",
+        db_sync, kind="test", status="running",
         started_at=now - timedelta(minutes=50),
     )
     db_sync.commit()