Reusable link box (Jinja macro in _macros.html + shared JS/CSS/QR lib in
base.html): a 'Link' button toggles the URL (with copy) and a 'QR' button toggles
a lazily-rendered QR of the same link — both hidden by default. Applied to the
profile address, profile groups & channels, and the profile cards on the list
pages. Centralize robustCopy in base.html; drop the per-page duplicates and the
old async group-link fetch (groups now use their known link).
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
