Tighten up the issue and change review pages

Tighten up the issue and change review pages

- Move contributor-branch CI approval from the Runs tab to the change
  request header, and return the allow form to that request.
- Put issue and change actions in the page header, right aligned with the
  title, instead of duplicating them in the sidebar.
- Drop sidebar details that repeated the header: state, author, age and
  reference. Keep labels, assignees, review base/head, approvals and checks.
- Consolidate approval status into one section and remove the empty-state
  line now covered by the count.
- Fix diff row spacing: keep pre-wrap on the code column only, so template
  whitespace in the gutter cells no longer creates blank lines.

Update the contributor CI test, the HTMX fragment expectations and the
documentation that named the Runs tab as the approval location.