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/App.tsx

@@ -8,6 +8,7 @@ import { analyticsService } from './services/analytics.service';
 import { GalleryAuthProvider, MaintenanceProvider } from './contexts';
 import { ThemeProvider } from './contexts/ThemeContext';
 import { GalleryPage } from './pages/GalleryPage';
+import { ClientAccessPage } from './pages/ClientAccessPage';
 import { PreviewPage } from './pages/gallery/PreviewPage';
 import { LegalPage } from './pages/public/LegalPage';
 import {
@@ -121,6 +122,11 @@ function App() {
                   <Routes>
                   {/* Public gallery routes */}
                   <Route path="/gallery/preview" element={<PreviewPage />} />
+                  <Route path="/gallery/:slug/client-access" element={
+                    <GalleryAuthProvider>
+                      <ClientAccessPage />
+                    </GalleryAuthProvider>
+                  } />
                   <Route path="/gallery/:slug/:token?" element={
                     <GalleryAuthProvider>
                       <GalleryPage />