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>

backend/app/tasks/backup.py

@@ -125,55 +125,6 @@ def backup_db_task(self, *, tag: str | None = None,
     return {"backup_run_id": run_id}
 
 
-@celery.task(
-    name="backend.app.tasks.backup.backup_images_task",
-    bind=True,
-    autoretry_for=(OperationalError, DBAPIError),
-    retry_backoff=30, retry_backoff_max=300, max_retries=1,
-    soft_time_limit=21600, time_limit=23400,
-)
-def backup_images_task(self, *, tag: str | None = None,
-                       triggered_by: str = "manual") -> dict:
-    """Create one images backup. Same shape as backup_db_task; uses
-    tar_path instead of sql_path."""
-    SessionLocal = _sync_session_factory()
-    now = datetime.now(UTC)
-    with SessionLocal() as session:
-        row = BackupRun(
-            kind="images", status="running", tag=tag,
-            triggered_by=triggered_by, started_at=now, manifest={},
-        )
-        session.add(row)
-        session.commit()
-        session.refresh(row)
-        run_id = row.id
-
-    try:
-        result = backup_service.backup_images(
-            images_root=IMAGES_ROOT,
-            tag=tag, triggered_by=triggered_by,
-        )
-    except (SoftTimeLimitExceeded, Exception) as exc:
-        with SessionLocal() as session:
-            row = session.get(BackupRun, run_id)
-            if row is not None:
-                _mark_failed(session, row, exc)
-        raise
-
-    with SessionLocal() as session:
-        row = session.get(BackupRun, run_id)
-        row.status = "ok"
-        row.finished_at = datetime.now(UTC)
-        row.tar_path = result["tar_path"]
-        row.size_bytes = result["size_bytes"]
-        row.manifest = {
-            "manifest_path": result["manifest_path"],
-            "ts": result["ts"],
-        }
-        session.commit()
-    return {"backup_run_id": run_id}
-
-
 @celery.task(
     name="backend.app.tasks.backup.restore_db_task",
     bind=True,
@@ -225,52 +176,6 @@ def restore_db_task(self, *, source_backup_run_id: int) -> dict:
     return {"backup_run_id": marker_id}
 
 
-@celery.task(
-    name="backend.app.tasks.backup.restore_images_task",
-    bind=True, max_retries=0,
-    soft_time_limit=21600, time_limit=23400,
-)
-def restore_images_task(self, *, source_backup_run_id: int) -> dict:
-    """Mirrors restore_db_task; uses backup_service.restore_images."""
-    SessionLocal = _sync_session_factory()
-    now = datetime.now(UTC)
-    with SessionLocal() as session:
-        src = session.get(BackupRun, source_backup_run_id)
-        if src is None or src.kind != "images" or not src.tar_path:
-            raise ValueError(
-                f"BackupRun id={source_backup_run_id} is not a valid images backup"
-            )
-        marker = BackupRun(
-            kind="images", status="restoring",
-            triggered_by="restore", started_at=now,
-            restored_from_id=src.id,
-            manifest={"source_tar_path": src.tar_path},
-        )
-        session.add(marker)
-        session.commit()
-        session.refresh(marker)
-        marker_id = marker.id
-        tar_path = src.tar_path
-
-    try:
-        backup_service.restore_images(
-            images_root=IMAGES_ROOT, tar_path=Path(tar_path),
-        )
-    except (SoftTimeLimitExceeded, Exception) as exc:
-        with SessionLocal() as session:
-            row = session.get(BackupRun, marker_id)
-            if row is not None:
-                _mark_failed(session, row, exc)
-        raise
-
-    with SessionLocal() as session:
-        row = session.get(BackupRun, marker_id)
-        row.status = "restored"
-        row.finished_at = datetime.now(UTC)
-        session.commit()
-    return {"backup_run_id": marker_id}
-
-
 @celery.task(
     name="backend.app.tasks.backup.prune_backups",
     soft_time_limit=300, time_limit=600,
@@ -278,27 +183,23 @@ def restore_images_task(self, *, source_backup_run_id: int) -> dict:
 def prune_backups() -> dict:
     """Daily Beat. Per-kind retention from ImportSettings.
 
-    Returns {"db_deleted": N, "images_deleted": M, "media_deleted": L,
-    "restore_deleted": R, "reconcile_deleted": C, "test_deleted": T,
+    Returns {"db_deleted": N, "media_deleted": L, "restore_deleted": R, "reconcile_deleted": C, "test_deleted": T,
     "files_unlinked": K}. Media, restore, reconcile and test runs leave no
     files here; only their history is trimmed, to the latest MEDIA_RUNS_KEPT,
     RESTORE_RUNS_KEPT, RECONCILE_RUNS_KEPT and TEST_RUNS_KEPT.
     Tagged rows (tag IS NOT NULL) are never pruned.
     Status='running' / 'restoring' rows are never pruned — the
     recover_stalled_backup_runs sweep flips truly-stuck ones to
-    'error' first. (Earlier docstring claimed the FC-3i TaskRun sweep
-    handled those, but TaskRun cleanup never touched BackupRun rows.
-    Audit 2026-06-02 added the dedicated sweep.)
+    'error' first.
     """
     SessionLocal = _sync_session_factory()
-    counts = {"db_deleted": 0, "images_deleted": 0, "media_deleted": 0,
+    counts = {"db_deleted": 0, "media_deleted": 0,
               "restore_deleted": 0, "reconcile_deleted": 0, "test_deleted": 0,
               "files_unlinked": 0}
     with SessionLocal() as session:
         s = ImportSettings.load_sync(session)
         for kind, keep in (
             ("db", s.backup_db_keep_last_n),
-            ("images", s.backup_images_keep_last_n),
             ("media", MEDIA_RUNS_KEPT),
             ("restore", RESTORE_RUNS_KEPT),
             ("reconcile", RECONCILE_RUNS_KEPT),
@@ -315,7 +216,6 @@ def prune_backups() -> dict:
             for row in candidates:
                 result = backup_service.unlink_artifact_files(
                     sql_path=row.sql_path,
-                    tar_path=row.tar_path,
                     manifest_path=(row.manifest or {}).get("manifest_path"),
                 )
                 counts["files_unlinked"] += sum(