feat(frontend): dedupe /public/settings via shared usePublicSettings hook (#325)

Pre-dedup: 7 calls to /api/public/settings on a single /admin/login page
load — 4 from raw-fetch consumers + 3 from React Query consumers using
inconsistent queryKeys. Captured live in Chrome DevTools.

Post-dedup: 1 call. Verified by tests/e2e/public-settings-dedup.spec.ts.

Adds:
- frontend/src/hooks/usePublicSettings.ts — single React Query hook,
  60s staleTime, queryKey ['public-settings']. Vitest with mocked api
  proves multi-mount dedup.
- Extended PublicSettings interface with seo_meta_* fields used by
  RobotsMetaTags and branding_logo_* fields used by GalleryView/AdminHeader.

Migrates 19 call sites across 4 risk-ordered rounds:
- Round A (high fan-in): GlobalThemeProvider, MaintenanceContext (with
  refetchInterval to preserve maintenance polling), MaintenanceWrapper
  (drops the now-redundant per-route ping; axios interceptor already
  handles 503), AdminHeader.
- Round B (gallery/login): GalleryView, GalleryPage, ClientAccessPage,
  AdminLoginPage, MaintenanceMode.
- Round C (decorative): RobotsMetaTags, DynamicFavicon, CMSContentBlock,
  ReCaptcha, useWatermarkSettings (rips out raw fetch + local state),
  LegalPage.
- Round D (queryKey alignment): useLocalizedDate, UserPhotoUpload,
  CreateEventPage. EventDetailsPage Round D ships in the follow-up
  commit that adds presigned-download UI on the same page.

App.tsx (AnalyticsBootstrap) and EventDetailsPage are deferred to
later commits — both files mix #325 changes with backend feature work.

frontend/src/pages/ClientAccessPage.tsx

@@ -2,12 +2,11 @@ import React, { useState } from 'react';
 import { useParams, useSearchParams, useNavigate, Link } from 'react-router-dom';
 import { AlertCircle, Lock } from 'lucide-react';
 import { useTranslation } from 'react-i18next';
-import { useQuery } from '@tanstack/react-query';
 
 import { Card, CardContent, Input, Button, Loading } from '../components/common';
 import { useGalleryAuth } from '../contexts';
 import { useGalleryInfo } from '../hooks/useGallery';
-import { api } from '../config/api';
+import { usePublicSettings } from '../hooks/usePublicSettings';
 import { buildResourceUrl } from '../utils/url';
 
 export const ClientAccessPage: React.FC = () => {
@@ -22,14 +21,7 @@ export const ClientAccessPage: React.FC = () => {
 
   const { data: galleryInfo, isLoading: isLoadingInfo, error: infoError } = useGalleryInfo(slug);
 
-  const { data: settingsData } = useQuery({
-    queryKey: ['gallery-settings'],
-    queryFn: async () => {
-      const response = await api.get('/public/settings');
-      return response.data;
-    },
-    staleTime: 5 * 60 * 1000,
-  });
+  const { data: settingsData } = usePublicSettings();
 
   // If already authenticated as client, redirect to gallery
   React.useEffect(() => {

frontend/src/pages/GalleryPage.tsx

@@ -4,7 +4,7 @@ import { AlertCircle, Clock } from 'lucide-react';
 import { differenceInDays, parseISO } from 'date-fns';
 import { useTranslation } from 'react-i18next';
 import { useLocalizedDate } from '../hooks/useLocalizedDate';
-import { useQuery } from '@tanstack/react-query';
+import { usePublicSettings } from '../hooks/usePublicSettings';
 
 import { Card, CardContent, Input, Button, ReCaptcha, CMSContentBlock } from '../components/common';
 import { useGalleryAuth, useTheme } from '../contexts';
@@ -13,7 +13,6 @@ import { GalleryView } from '../components/gallery';
 import { GallerySkeleton } from '../components/gallery/GallerySkeleton';
 import { analyticsService } from '../services/analytics.service';
 import { galleryService } from '../services';
-import { api } from '../config/api';
 import { GALLERY_THEME_PRESETS } from '../types/theme.types';
 import { buildResourceUrl } from '../utils/url';
 import { isGalleryPublic, normalizeRequirePassword } from '../utils/accessControl';
@@ -106,15 +105,7 @@ export const GalleryPage: React.FC = () => {
     setAutoLoginAttempted(false);
   }, [resolvedSlug]);
   
-  // Fetch branding settings
-  const { data: settingsData, isLoading: isLoadingSettings } = useQuery({
-    queryKey: ['gallery-settings'],
-    queryFn: async () => {
-      const response = await api.get('/public/settings');
-      return response.data;
-    },
-    staleTime: 5 * 60 * 1000, // Cache for 5 minutes
-  });
+  const { data: settingsData, isLoading: isLoadingSettings } = usePublicSettings();
   
   // Set language from admin settings when on login page
   React.useEffect(() => {

frontend/src/pages/admin/AdminLoginPage.tsx

@@ -2,12 +2,12 @@ import React, { useState, useEffect } from 'react';
 import { Navigate, useSearchParams } from 'react-router-dom';
 import { Lock, Mail, Eye, EyeOff, AlertCircle } from 'lucide-react';
 import { toast } from 'react-toastify';
-import { useQuery } from '@tanstack/react-query';
 import { useTranslation } from 'react-i18next';
 
 import { Button, Input, Card, ReCaptcha } from '../../components/common';
 import { useAdminAuth } from '../../contexts';
 import { authService } from '../../services/auth.service';
+import { usePublicSettings } from '../../hooks/usePublicSettings';
 import { api } from '../../config/api';
 
 export const AdminLoginPage: React.FC = () => {
@@ -25,15 +25,7 @@ export const AdminLoginPage: React.FC = () => {
   const [loginSuccess, setLoginSuccess] = useState(false);
   const [recaptchaToken, setRecaptchaToken] = useState<string | null>(null);
 
-  // Fetch branding settings (unauthenticated)
-  const { data: settingsData } = useQuery({
-    queryKey: ['admin-login-settings'],
-    queryFn: async () => {
-      const response = await api.get('/public/settings');
-      return response.data;
-    },
-    staleTime: 5 * 60 * 1000, // Cache for 5 minutes
-  });
+  const { data: settingsData } = usePublicSettings();
 
   const companyName = settingsData?.branding_company_name?.trim() || 'PicPeak';
   const logoUrl = settingsData?.branding_logo_url?.trim();

frontend/src/pages/admin/CreateEventPage.tsx

@@ -22,7 +22,7 @@ import { eventsService } from '../../services/events.service';
 import { useLocalizedDate } from '../../hooks/useLocalizedDate';
 import { categoriesService } from '../../services/categories.service';
 import { settingsService } from '../../services/settings.service';
-import { publicSettingsService } from '../../services/publicSettings.service';
+import { usePublicSettings } from '../../hooks/usePublicSettings';
 import { cssTemplatesService } from '../../services/cssTemplates.service';
 import { eventTypesService } from '../../services/eventTypes.service';
 import { useTranslation } from 'react-i18next';
@@ -170,11 +170,7 @@ export const CreateEventPage: React.FC = () => {
     queryFn: () => settingsService.getAllSettings()
   });
 
-  // Fetch public settings for field requirements
-  const { data: publicSettings } = useQuery({
-    queryKey: ['public-settings'],
-    queryFn: () => publicSettingsService.getPublicSettings()
-  });
+  const { data: publicSettings } = usePublicSettings();
 
   // Get field requirements (default to true if not set)
   const requireCustomerName = publicSettings?.event_require_customer_name !== false;

frontend/src/pages/public/LegalPage.tsx

@@ -6,7 +6,7 @@ import { ArrowLeft, Home } from 'lucide-react';
 import DOMPurify from 'dompurify';
 import { Loading, Card } from '../../components/common';
 import { cmsService } from '../../services/cms.service';
-import { api } from '../../config/api';
+import { usePublicSettings } from '../../hooks/usePublicSettings';
 import '../../styles/prose-overrides.css';
 
 export const LegalPage: React.FC = () => {
@@ -18,15 +18,7 @@ export const LegalPage: React.FC = () => {
   const pathname = window.location.pathname;
   const pageSlug = slug || pathname.split('/').pop() || '';
   
-  // Fetch settings to get default language
-  const { data: settingsData } = useQuery({
-    queryKey: ['public-settings'],
-    queryFn: async () => {
-      const response = await api.get('/public/settings');
-      return response.data;
-    },
-    staleTime: 5 * 60 * 1000, // Cache for 5 minutes
-  });
+  const { data: settingsData } = usePublicSettings();
 
   // Use admin settings language
   const lang = settingsData?.default_language || 'en';