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

frontend/src/types/index.ts

@@ -55,8 +55,13 @@ export interface Event {
   css_template_id?: number | null;
   // Photo cap
   photo_cap?: number | null;
+  // Client access (#172)
+  client_access_enabled?: boolean;
+  client_share_token?: string;
 }
 
+export type GalleryAccessLevel = 'guest' | 'client';
+
 export interface GalleryInfo {
   event_name: string;
   event_type: string;
@@ -92,6 +97,8 @@ export interface Photo {
   audio_codec?: string;
   width?: number;
   height?: number;
+  // Visibility (#172)
+  visibility?: 'visible' | 'hidden';
   // Feedback fields
   has_feedback?: boolean;
   average_rating?: number;
@@ -206,6 +213,7 @@ export interface GalleryAuthResponse {
     require_password?: boolean;
     photo_cap?: number | null;
   };
+  accessLevel?: GalleryAccessLevel;
 }
 
 // API Error type