feat: Smart Shopping List + Household bugfixes

Shopping:
- Merged view (default): same ingredient + unit = summed amounts
  (150g Quark + 300g Quark → 450g Quark)
- Shows which recipes need each ingredient
- Toggle between 'Zusammengefasst' and 'Nach Rezept' views
- Alphabetically sorted in merged view

Household bugfixes:
- Fixed bouncy modal animation (removed Framer Motion spring)
- Fixed clipboard copy on HTTP (textarea fallback)
- Fixed logout on join (JWT secrets mismatch in docker-compose)

Also: mounted backend data/ volume for recipe images

frontend/nginx.conf

@@ -4,6 +4,14 @@ server {
     root /usr/share/nginx/html;
     index index.html;
 
+    # Image proxy to backend
+    location /images/ {
+        proxy_pass http://backend:6001;
+        proxy_set_header Host $host;
+        expires 30d;
+        add_header Cache-Control "public, immutable";
+    }
+
     # API proxy to backend
     location /api/ {
         proxy_pass http://backend:6001;