Bite-sized implementation plan for spec 0002 (case-page half of #14):
add a gated "Kopieren + Schließen" control below the document (Task 1,
with a shared copyDocText() refactor), a bare "Schließen" for
documentless open cases (Task 2), then remove the H1 trash-can close
(Task 3), and a whole-suite + clippy + fmt gate (Task 4). Ordered so
each task leaves the suite green.
refs #14
