New route with server load function (reads URL params, derives unreadCount from
the page, single API call per Sara's architecture requirement), mark-all form
action, and the full page UI: filter pills with ARIA radiogroup, notification
rows with border+dot unread indicators (WCAG 1.4.1), "Ältere laden" client-side
append, and empty state. Includes all de/en/es translation keys.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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