- test_render_marketplaces_filtered_by_rbac: seeds 2 marketplaces, 2 groups,
grants, 2 users; asserts each user's rendered output references only their
group's marketplace/plugins, not the other's (I-3).
- test_validation_stub_matches_build_context_shape in test_welcome_template_api.py:
asserts _VALIDATION_STUB_CONTEXT top-level and nested keys (instance, server,
user) match build_context() output so stub drift is caught in CI (I-4).
- test_validation_stub_matches_build_context_shape in test_setup_banner_api.py:
same shape check against build_setup_banner_context() (I-4).
Adds an optional Jinja2/HTML banner displayed above the bootstrap
commands on /setup. Empty by default; admin authors it at
/admin/setup-banner. autoescape=True — safe for HTML context.
Render failures return "" so a broken banner never breaks /setup.
Schema v22: setup_banner singleton table, auto-migration v21→v22.
