~x-ai/grok-latest → A (8:1)

Commit A consolidates duplicated test harness, HTTP/OAuth mocks, registration helpers, cargo build, and server env into shared modules (common.bb/oauth.bb), shrinking auth/grants/integration and improving maintainability. Commit B only relocates the delete control into post_header_meta with flex CSS tweaks—presentational churn with little lasting design impact.