fix(BA-5822): re-anchor drop-legacy-AppConfig migration to latest main head

origin/main has progressed past ad7acfe8aa1c since this migration
landed; chain `84d5c6daf8cc` after the current main head
`ce69b746304e` so the alembic chain stays linear (single head). No
schema change.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: jopemachine

src/ai/backend/manager/models/alembic/versions/84d5c6daf8cc_drop_legacy_app_configs_table.py

@@ -8,7 +8,7 @@
 different unique key) so no in-place data migration is attempted.
 
 Revision ID: 84d5c6daf8cc
-Revises: ad7acfe8aa1c
+Revises: ce69b746304e
 Create Date: 2026-04-24
 
 """
@@ -21,7 +21,7 @@
 
 # revision identifiers, used by Alembic.
 revision = "84d5c6daf8cc"
-down_revision = "ad7acfe8aa1c"
+down_revision = "ce69b746304e"
 # Part of: 26.5.0
 branch_labels = None
 depends_on = None