feat(branding): symmetric light/dark logo fallback + customer surface

Pick the logo by the active color mode with a symmetric fallback: a
single uploaded logo serves both modes (dark uses dark||light, light
uses light||dark). Apply to admin header, customer gallery, and the
customer portal (follows branding_force_color_mode). PDFs already use
the light branding logo with the business-profile PDF logo as override
(resolveLogoFile) — unchanged.

frontend/src/components/admin/AdminHeader.tsx

@@ -33,10 +33,11 @@ export const AdminHeader: React.FC<AdminHeaderProps> = ({ onMenuClick }) => {
   const { data: brandingSettings } = usePublicSettings();
 
   const companyName = brandingSettings?.branding_company_name?.trim() || 'PicPeak';
-  // Dark-mode logo variant: use it when the admin theme is dark and a dark
-  // logo was uploaded; otherwise fall back to the light logo.
-  const logoUrl = (isDark && brandingSettings?.branding_logo_url_dark?.trim())
-    || brandingSettings?.branding_logo_url?.trim();
+  // Dark-mode logo variant. Symmetric fallback: if only one logo is set,
+  // use it for both modes (dark → dark||light, light → light||dark).
+  const lightLogo = brandingSettings?.branding_logo_url?.trim();
+  const darkLogo = brandingSettings?.branding_logo_url_dark?.trim();
+  const logoUrl = isDark ? (darkLogo || lightLogo) : (lightLogo || darkLogo);
   const logoDisplayMode = brandingSettings?.branding_logo_display_mode || 'logo_and_text';
   // Logo placement honours the same Branding > Logo Position setting
   // the gallery does. 'sidepanel' moves the logo into the AdminSidebar

frontend/src/components/gallery/GalleryLayout.tsx

@@ -123,9 +123,11 @@ export const GalleryLayout: React.FC<GalleryLayoutProps> = ({
   const { t } = useTranslation();
   const { format } = useLocalizedDate();
   const { theme } = useTheme();
-  // Dark-mode logo variant: prefer it on dark gallery themes, else light.
-  const brandLogoUrl = (theme.colorMode === 'dark' && brandingSettings?.logo_url_dark)
-    || brandingSettings?.logo_url;
+  // Dark-mode logo variant. Symmetric fallback: a single uploaded logo
+  // serves both modes (dark → dark||light, light → light||dark).
+  const brandLogoUrl = theme.colorMode === 'dark'
+    ? (brandingSettings?.logo_url_dark || brandingSettings?.logo_url)
+    : (brandingSettings?.logo_url || brandingSettings?.logo_url_dark);
   const guestIdentity = useGuestIdentityOptional();
 
   // Footer legal-link config. Cached aggressively because the toggle state

frontend/src/pages/customer/CustomerLayout.tsx

@@ -65,7 +65,16 @@ export const CustomerLayout: React.FC = () => {
   const [sidebarOpen, setSidebarOpen] = useState(false);
 
   const companyName = settingsData?.branding_company_name?.trim() || 'PicPeak';
-  const logoUrl = settingsData?.branding_logo_url?.trim();
+  // Theme-aware logo: the customer surface follows branding_force_color_mode
+  // ('auto' → OS preference). Symmetric fallback so a single uploaded logo
+  // serves both modes.
+  const forceMode = settingsData?.branding_force_color_mode;
+  const customerIsDark = forceMode === 'dark'
+    || (forceMode === 'auto' && typeof window !== 'undefined'
+        && window.matchMedia?.('(prefers-color-scheme: dark)').matches);
+  const lightLogo = settingsData?.branding_logo_url?.trim();
+  const darkLogo = settingsData?.branding_logo_url_dark?.trim();
+  const logoUrl = customerIsDark ? (darkLogo || lightLogo) : (lightLogo || darkLogo);
   const resolvedLogoUrl = logoUrl || '/picpeak-logo-transparent.png';
 
   // Filter out feature-gated entries the customer can't see. Galleries +