The header edit/read toggle now controls only the current session's mode
without saving it as the user's preference. The saved preference (set in
profile settings) is applied once on initial load and sticks across page
navigations within the session, so navigating to a new page no longer
resets the mode mid-session.
Fixes#1693
Replace UnstyledButton with UnstyledButton component={Link} so each
notification renders as a real anchor element. Regular left-clicks use
SPA navigation and close the popover; Ctrl/Cmd/middle-click open the
page in a new tab. All click types mark the notification as read.
The copy-link decoration widget (contentEditable="false") injected
inside headings prevented browsers from deleting the last remaining
character via Backspace or Delete keys. Only show the widget when the
heading has more than one character of content.
Julien Fontanet