feat: add photo cap per event and Portuguese (pt-BR) locale

- Add photo_cap column to events table (migration 074) to limit photos per event
- Enforce photo cap in upload route, returning 400 when limit exceeded
- Pass photo_cap through all event CRUD routes and frontend forms
- Add complete Portuguese (pt-BR) translation (2300+ strings)
- Register pt locale in i18n config, language selector, date formatting
- Add photoCap/photoCapHelp translation keys to all locale files (en, de, ru, pt)

frontend/src/services/events.service.ts

@@ -39,6 +39,7 @@ interface CreateEventData {
   require_name_email?: boolean;
   moderate_comments?: boolean;
   show_feedback_to_guests?: boolean;
+  photo_cap?: number | null;
 }
 
 interface UpdateEventData {
@@ -58,6 +59,7 @@ interface UpdateEventData {
   hero_photo_id?: number | null;
   source_mode?: 'managed' | 'reference';
   external_path?: string | null;
+  photo_cap?: number | null;
 }
 
 interface EventsListResponse {