Improved drawing sync: MIME detection, WebP/JPEG support, sync log + frontend updates

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

frontend/nginx.conf

@@ -4,26 +4,26 @@ server {
     root /usr/share/nginx/html;
     index index.html;
 
-    # Allow large drawing data + body size
     client_max_body_size 50m;
 
-    # PWA service worker — MUST not be cached by browser/proxy
+    # PWA service worker — never cache
     location = /sw.js {
         add_header Cache-Control "no-cache, no-store, must-revalidate";
         add_header Pragma "no-cache";
+        add_header Expires "0";
         add_header Service-Worker-Allowed "/";
-        add_header Content-Type "application/javascript";
+        types { application/javascript js; }
         try_files $uri =404;
     }
 
     # PWA manifest
     location = /manifest.json {
-        add_header Cache-Control "public, max-age=3600";
-        add_header Content-Type "application/manifest+json";
+        add_header Cache-Control "no-cache";
+        types { application/manifest+json json; }
         try_files $uri =404;
     }
 
-    # Static assets — long cache with content hash from Vite
+    # Vite hashed assets — immutable cache
     location /assets/ {
         add_header Cache-Control "public, max-age=31536000, immutable";
         try_files $uri =404;
@@ -35,8 +35,9 @@ server {
         try_files $uri =404;
     }
 
-    # SPA fallback — all other routes serve index.html
+    # SPA fallback
     location / {
+        add_header Cache-Control "no-cache";
         try_files $uri $uri/ /index.html;
     }