fix: suppress Alembic CodeQL false positives

[suguanYang]

Summary

• Change the three migration __all__ declarations from annotated assignments to plain list assignments.
• Preserve Alembic's required revision, down_revision, branch_labels, and depends_on metadata.

Why

The CodeQL py/unused-global-variable query recognizes names exported through a simple __all__ assignment, but not the annotated __all__: list[str] = ... form. This keeps the quality check enabled elsewhere without adding per-line suppressions or removing required migration metadata.

Verification

• uv run ruff check on all three migrations
• uv run pyright on all three migrations
• git diff --check