fix: reliably intercept extension update/uninstall + polish backup screen
The full-screen pre-action backup did not fire for extension
updates/uninstalls because Joomla 6 renders the com_installer toolbar
Update/Uninstall buttons as `<button task="update.update">` web
components, not inline onclick="Joomla.submitbutton(...)". Wrapping
Joomla.submitbutton never caught them.
installer-backup.js now uses a capture-phase document click listener on
any `[task]` element matching update.update / manage.remove(/uninstall),
so it runs before the toolbar web component. It captures the checked
cid[] selection, runs the full-screen backup, and on return restores the
selection, sets the boxchecked list-guard field, and re-fires the real
toolbar button with __msbResuming set so it is not re-intercepted.
Also polishes the runbackup screen: the progress bar is now a full-bleed
strip along the bottom edge of the card (edge-to-edge, clipped to the
rounded corners) instead of a boxed bar crowding the status text, and it
is coloured from the Atum template CSS custom properties
(--template-link-color / --template-special-color / --template-success-color
/ --template-danger-color) with Bootstrap and literal fallbacks.
Claude-Session: https://claude.ai/code/session_01WbGBN9VyRK61zczYWcCQ2i
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