fix(ansible): shorten migration 0012 revision id to fit alembic_version(32)

The id 0012_ansible_run_triggered_by_nullable was 38 chars; alembic_version.
version_num is VARCHAR(32), so stamping it raised StringDataRightTruncationError
and the boot/migrate integration lane failed. Renamed to 0012_ansible_run_nullable.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

steward/migrations/versions/0012_ansible_run_nullable.py

@@ -1,14 +1,16 @@
 """Make ansible_runs.triggered_by nullable (automated runs have no user)
 
-Revision ID: 0012_ansible_run_triggered_by_nullable
+Revision ID: 0012_ansible_run_nullable
 Revises: 0011_audit_log
 Create Date: 2026-06-02
+
+Note: the revision id is kept <=32 chars to fit alembic_version.version_num.
 """
 from typing import Sequence, Union
 from alembic import op
 import sqlalchemy as sa
 
-revision: str = "0012_ansible_run_triggered_by_nullable"
+revision: str = "0012_ansible_run_nullable"
 down_revision: Union[str, None] = "0011_audit_log"
 branch_labels: Union[str, Sequence[str], None] = None
 depends_on: Union[str, Sequence[str], None] = None