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/mobile-nav.tsx

@@ -34,7 +34,11 @@ export function MobileNav({ children }: { children: React.ReactNode }) {
         <div
           className="fixed inset-0 z-30 md:hidden"
           onClick={() => setOpen(false)}
-          style={{ backgroundColor: "rgba(0,0,0,0.4)" }}
+          style={{
+            backgroundColor: "rgba(0,0,0,0.45)",
+            backdropFilter: "blur(6px)",
+            WebkitBackdropFilter: "blur(6px)",
+          }}
         />
       )}