Mobile-responsive: task cards, detail panel, sticky header

- TaskCard: hide action buttons on mobile (tap to open detail panel), smaller text/badges, word-break titles
- TaskDetailPanel: full-screen on mobile with Back button, responsive padding, stacked timeline, hidden UUID on small screens
- QueuePage: sticky header offset for mobile nav bar (top-14)
- Priority/source grid stacks vertically on mobile

frontend/src/pages/QueuePage.tsx

@@ -65,7 +65,7 @@ export function QueuePage() {
   return (
     <div className="min-h-screen">
       {/* Page Header */}
-      <header className="bg-white border-b border-gray-200 sticky top-0 md:top-0 z-30">
+      <header className="bg-white border-b border-gray-200 sticky top-14 md:top-0 z-30">
         <div className="max-w-4xl mx-auto px-4 sm:px-6 py-3 sm:py-4 flex items-center justify-between">
           <div>
             <h1 className="text-lg sm:text-xl font-bold text-gray-900">Task Queue</h1>