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)

backend/src/utils/dateFormatter.js

@@ -54,6 +54,8 @@ async function formatDate(date, language = 'en') {
     let locale = dateConfig.locale || 'en-GB';
     if (language === 'de') {
       locale = 'de-DE';
+    } else if (language === 'pt') {
+      locale = 'pt-BR';
     } else if (language === 'en' && dateConfig.format === 'MM/DD/YYYY') {
       locale = 'en-US';
     }