Import slugify_or_default from hub-core, add contract tests, vendor hub-core in
Docker/Forgejo CI, document metadata isolation and pagination deferral, and
align INTENT/SCOPE with three-repo stack.
Correct related_to IDs for inter-hub and whynot-design successors,
document src/core_hub FastAPI scaffold and pytest evidence, and
keep availability at A1 until production cutover is proven.