feat: photo visibility control with client access (#172)

Add two-tier gallery access system allowing clients (e.g., wedding couples) to
review and hide photos before the gallery is shared with guests.

Backend:
- Migration 074: add visibility column to photos, client_access_enabled/
  client_password_hash/client_share_token to events
- Client login endpoint (POST /auth/gallery/:slug/client-login) with bcrypt PIN
- Gallery photo list filters hidden photos for guests, shows all for clients
- Visibility toggle endpoints (single + bulk) for client access level
- Admin event CRUD supports client access fields
- Email template includes client access link + PIN (EN/DE/RU/PT)

Frontend:
- ClientAccessPage: PIN entry form at /gallery/:slug/client-access
- GalleryView: client mode banner, visibility counter, toggle controls
- GridGalleryLayout: eye/eye-off overlay per photo for clients
- AdminPhotoGrid: visibility badge, bulk Hide/Show buttons
- EventDetailsPage: Client Access settings section (toggle, PIN, link)
- CreateEventPage: client access toggle + PIN in event creation form
- GalleryAuthContext: accessLevel/isClient/clientLogin support
- New complete pt-BR locale (pt.json) with all translations
- Client access i18n keys for EN, DE, RU, PT

backend/src/middleware/gallery.js

@@ -102,8 +102,9 @@ async function verifyGalleryAccess(req, res, next) {
     
     logger.debug('[verifyGalleryAccess] Event located', { eventId: event.id, slug: event.slug });
     req.event = event;
+    req.accessLevel = decoded.accessLevel || 'guest';
     req.sessionID = decoded.sessionId || `gallery_${event.id}_${Date.now()}`;
-    
+
     // Create client info for logging (similar to secureImageMiddleware but simpler)
     req.clientInfo = {
       ip: req.ip || req.connection.remoteAddress || 'unknown',