fix: improve backdrop blur visibility on dropdowns and overlays

- Reduce dropdown background opacity from 97% to 80% so backdrop-filter is visible
- Add glass-dropdown CSS class with blur(16px) and saturate(180%)
- Add backdrop blur to mobile nav overlay for smoother feel
- Increase photo lightbox backdrop blur from 2px to 8px
- Add background-blend-mode: overlay to site-bg for richer texture

src/components/public/photo-lightbox.tsx

@@ -97,7 +97,7 @@ export function PhotoLightbox({ photos }: { photos: LightboxPhoto[] }) {
             justifyContent: "center",
             padding: "1.5rem",
             background: "rgba(0, 0, 0, 0.82)",
-            backdropFilter: "blur(2px)",
+            backdropFilter: "blur(8px)",
             cursor: "zoom-out",
           }}
         >