On mobile (<=640px), the header right section was too crowded with icons.
Now hides notification bell, share panel, and settings gear buttons, and
adds equivalent mobile-only items in the identity dropdown menu. Share
uses native navigator.share() when available.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Extract canvas inline share panel into reusable <rstack-share-panel> web component
and add it to the shell header between notification bell and settings gear. Canvas
now uses the component too, removing ~230 lines of inline HTML/CSS/JS.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Jeff Emmett