fix(web): show dialogs opened from settings on top of the settings page

The settings modal is a full-screen OPAQUE overlay at z-index 500. Dialogs
opened from within it (share, add-account, color picker) share z-index 500 but
sit earlier in the DOM, so they rendered BEHIND the opaque settings page — the
Share button appeared to "do nothing". Drop the settings page to z-index 400 so
real modals stack above it. v79.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/js/version.js

@@ -1,2 +1,2 @@
 // Increment APP_VERSION with every code change
-export const APP_VERSION = 'v78';
+export const APP_VERSION = 'v79';