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/api/system_backup.py

@@ -1,5 +1,5 @@
-"""FC-3h: /api/system/backup — create/list/restore/delete/tag for
-DB + image backups.
+"""/api/system/backup: database dumps, the off-site destination and its media
+backup, restores, test restores, and the run history.
 
 Read endpoints are public on FC (operator-facing internal API; same
 posture as /api/system/activity). Write endpoints take a typed
@@ -20,13 +20,12 @@ system_backup_bp = Blueprint(
     "system_backup", __name__, url_prefix="/api/system/backup",
 )
 
-_KINDS = frozenset({"db", "images", "media", "restore", "reconcile", "test"})
+_KINDS = frozenset({"db", "media", "restore", "reconcile", "test"})
 _TAG_MAX_LEN = 64
 _BACKUP_SETTINGS_FIELDS = (
     "backup_db_nightly_enabled",
     "backup_db_nightly_hour_utc",
     "backup_db_keep_last_n",
-    "backup_images_keep_last_n",
 )
 
 
@@ -44,7 +43,6 @@ def _row_to_dict(r: BackupRun) -> dict:
             if r.finished_at and r.started_at else None
         ),
         "sql_path": r.sql_path,
-        "tar_path": r.tar_path,
         "size_bytes": r.size_bytes,
         "error": r.error,
         "restored_from_id": r.restored_from_id,
@@ -81,10 +79,6 @@ def _validate_backup_settings_patch(body: dict):
         v = body["backup_db_keep_last_n"]
         if not isinstance(v, int) or isinstance(v, bool) or not (1 <= v <= 365):
             return _bad("invalid_value", detail="backup_db_keep_last_n must be 1..365")
-    if "backup_images_keep_last_n" in body:
-        v = body["backup_images_keep_last_n"]
-        if not isinstance(v, int) or isinstance(v, bool) or not (1 <= v <= 100):
-            return _bad("invalid_value", detail="backup_images_keep_last_n must be 1..100")
     return None
 
 
@@ -99,17 +93,6 @@ async def trigger_db_backup():
     return jsonify({"status": "dispatched"}), 202
 
 
-@system_backup_bp.route("/images", methods=["POST"])
-async def trigger_images_backup():
-    body = await request.get_json(silent=True) or {}
-    tag = _validate_tag(body.get("tag"))
-    if isinstance(tag, tuple):
-        return tag
-    from ..tasks.backup import backup_images_task
-    backup_images_task.delay(tag=tag, triggered_by="manual")
-    return jsonify({"status": "dispatched"}), 202
-
-
 @system_backup_bp.route("/media", methods=["POST"])
 async def trigger_media_backup():
     """Send the images and attachments not yet in the off-site bucket. Refused
@@ -348,17 +331,17 @@ async def trigger_restore(run_id: int):
         row = await session.get(BackupRun, run_id)
         if row is None:
             return _bad("not_found", status=404)
-        if row.status != "ok":
-            return _bad(
-                "not_restorable",
-                detail=f"source backup status={row.status!r}; only 'ok' rows are restorable",
-            )
         if (row.manifest or {}).get("offsite"):
             return _bad(
                 "not_restorable",
                 detail=("this dump is kept in the off-site bucket, not on this server, "
                         "so it can't be restored from here"),
             )
+        if row.kind != "db" or row.status != "ok" or not row.sql_path:
+            return _bad(
+                "not_restorable",
+                detail="only a finished database dump kept on this server can be restored here",
+            )
         expected = f"restore-{row.kind}-{row.id}"
         if supplied != expected:
             return _bad(
@@ -366,15 +349,10 @@ async def trigger_restore(run_id: int):
                 detail=f"confirm must equal {expected!r}",
                 expected=expected,
             )
-        kind = row.kind
 
-    if kind == "db":
-        from ..tasks.backup import restore_db_task
-        restore_db_task.delay(source_backup_run_id=run_id)
-    else:  # 'images' (the only other value _KINDS allows via the trigger path)
-        from ..tasks.backup import restore_images_task
-        restore_images_task.delay(source_backup_run_id=run_id)
-    return jsonify({"status": "dispatched", "kind": kind}), 202
+    from ..tasks.backup import restore_db_task
+    restore_db_task.delay(source_backup_run_id=run_id)
+    return jsonify({"status": "dispatched", "kind": "db"}), 202
 
 
 @system_backup_bp.route("/runs/<int:run_id>/test", methods=["POST"])
@@ -414,7 +392,7 @@ async def delete_run(run_id: int):
             )
         from ..services import backup_service
         backup_service.unlink_artifact_files(
-            sql_path=row.sql_path, tar_path=row.tar_path,
+            sql_path=row.sql_path,
             manifest_path=(row.manifest or {}).get("manifest_path"),
         )
         await session.delete(row)
@@ -430,7 +408,6 @@ async def get_settings():
         "backup_db_nightly_enabled": row.backup_db_nightly_enabled,
         "backup_db_nightly_hour_utc": row.backup_db_nightly_hour_utc,
         "backup_db_keep_last_n": row.backup_db_keep_last_n,
-        "backup_images_keep_last_n": row.backup_images_keep_last_n,
     })