feat: centralize popup texts in new admin tab /admin/popups

- New admin page for shared popup texts (success, waiting list, error, Instagram hint)
- Removed popup fields from MC and Open Day admin editors
- All SignupModals now read from centralized popups config
- Stored as "popups" section in DB with fallback defaults

src/components/sections/OpenDay.tsx

@@ -6,12 +6,14 @@ import { SectionHeading } from "@/components/ui/SectionHeading";
 import { Reveal } from "@/components/ui/Reveal";
 import { SignupModal } from "@/components/ui/SignupModal";
 import type { OpenDayEvent, OpenDayClass } from "@/lib/openDay";
+import type { SiteContent } from "@/types";
 
 interface OpenDayProps {
   data: {
     event: OpenDayEvent;
     classes: OpenDayClass[];
   };
+  popups?: SiteContent["popups"];
 }
 
 function formatDateRu(dateStr: string): string {
@@ -23,7 +25,7 @@ function formatDateRu(dateStr: string): string {
   });
 }
 
-export function OpenDay({ data }: OpenDayProps) {
+export function OpenDay({ data, popups }: OpenDayProps) {
   const { event, classes } = data;
   const [signup, setSignup] = useState<{ classId: number; label: string } | null>(null);
 
@@ -132,8 +134,10 @@ export function OpenDay({ data }: OpenDayProps) {
           subtitle={signup.label}
           endpoint="/api/open-day-register"
           extraBody={{ classId: signup.classId, eventId: event.id }}
-          successMessage={event.successMessage}
-          waitingMessage={event.waitingListText}
+          successMessage={popups?.successMessage}
+          waitingMessage={popups?.waitingListText}
+          errorMessage={popups?.errorMessage}
+          instagramHint={popups?.instagramHint}
         />
       )}
     </section>