feat: promote studio theme to default, add favicon, deep-linkable lightbox

- Studio aesthetic now the default dark/light theme
- Removed MonochromToggle and 3-way theme cycle
- Light mode uses warm Studio-toned palette
- Added favicon (icon.png, apple-touch-icon, PWA icons)
- Lightbox URL sync: #photo-N hash for shareable photo links
- Browser back closes lightbox, shared links open directly

app/layout.tsx

@@ -17,6 +17,9 @@ const siteDescription = 'A curated photography portfolio';
 export const metadata: Metadata = {
   title: siteTitle,
   description: siteDescription,
+  icons: {
+    apple: '/apple-touch-icon.png',
+  },
   openGraph: {
     title: siteTitle,
     description: siteDescription,