feat: add smart map view with location-level clustering

- /map page with Leaflet (CartoDB dark tiles)
- Photos clustered by city/country (not per-photo)
- /api/map endpoint with encrypted cover asset IDs
- Configurable via gallery.yaml (map: true/false)
- Conditional nav link in header
- CSP updated for Leaflet CDN and tile servers
- Theme-aware popups with cover thumbnails and album links

app/layout.tsx

@@ -38,7 +38,8 @@ export const metadata: Metadata = {
 };
 
 export default function RootLayout({ children }: { children: React.ReactNode }) {
-  const { theme } = getConfig();
+  const config = getConfig();
+  const { theme } = config;
   const fontsUrl = getGoogleFontsUrl(theme);
 
   // Inject theme values as CSS custom properties
@@ -78,6 +79,11 @@ export default function RootLayout({ children }: { children: React.ReactNode })
             <Link href="/about" className="header__nav-link">
               About
             </Link>
+            {config.map && (
+              <Link href="/map" className="header__nav-link">
+                Map
+              </Link>
+            )}
             <ThemeToggle />
           </nav>
         </header>