Apply glassmorphism effect to overlays and panels

- Header: semi-transparent white with backdrop blur
- Visit counter: frosted glass instead of dark overlay
- Mobile filter panel: translucent with blur
- BottomSheet: frosted glass background
- Footer: subtle glass effect

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

frontend/src/components/BottomSheet.tsx

@@ -89,7 +89,7 @@ export default function BottomSheet({ open, onClose, children }: BottomSheetProp
       {/* Sheet */}
       <div
         ref={sheetRef}
-        className="fixed bottom-0 left-0 right-0 z-50 md:hidden flex flex-col bg-white rounded-t-2xl shadow-2xl"
+        className="fixed bottom-0 left-0 right-0 z-50 md:hidden flex flex-col bg-white/85 backdrop-blur-xl rounded-t-2xl shadow-2xl"
         style={{
           height: `${height * 100}vh`,
           transition: dragging ? "none" : "height 0.3s cubic-bezier(0.2, 0, 0, 1)",