fix(ui): design-system consistency — typography, borders, admin IA, search removal

- typography: font-semibold/font-medium → font-bold throughout (card, dialog, empty-state, notification-bell, quiz-experience, questions-panel, profile-manage)
- borders: border → border-2 for content containers (leaderboard error, notifications page, quiz pass screen, quiz option tiles, learning-panel error)
- admin IA: remove Card-in-SectionPanel nesting from announce-panel, challenges-panel, physical-orders-panel; SectionPanel gains optional actions slot
- announce-panel: flat composer + live preview; history as flat list; cancel-edit button
- lockout: raw textarea → Textarea design-system component
- global-search: delete component and all references (feature removed)
- progress.tsx: dir="ltr" for correct RTL fill direction; remove rtl:me-auto

frontend/src/components/ui/dialog.tsx

@@ -78,7 +78,7 @@ const DialogTitle = React.forwardRef<
 >(({ className, ...props }, ref) => (
   <DialogPrimitive.Title
     ref={ref}
-    className={cn("text-lg font-semibold leading-none tracking-tight", className)}
+    className={cn("text-lg font-bold leading-none tracking-tight", className)}
     {...props}
   />
 ));