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/hooks/useLocalizedDate.ts

@@ -1,6 +1,6 @@
 import { useTranslation } from 'react-i18next';
 import { format as dateFnsFormat, formatDistanceToNow as dateFnsFormatDistanceToNow } from 'date-fns';
-import { de, enUS } from 'date-fns/locale';
+import { de, enUS, ptBR } from 'date-fns/locale';
 import { useQuery } from '@tanstack/react-query';
 import { publicSettingsService } from '../services/publicSettings.service';
 
@@ -24,7 +24,9 @@ export const useLocalizedDate = () => {
   });
   
   const getLocale = () => {
-    return i18n.language === 'de' ? de : enUS;
+    if (i18n.language === 'de') return de;
+    if (i18n.language === 'pt' || i18n.language === 'pt-BR') return ptBR;
+    return enUS;
   };
   
   const format = (date: Date | string, formatStr?: string) => {