fix: WASM CDN defaults bypass Docker empty env vars, nginx redirect port issue

- Fix envOrDefault() to treat empty strings as unset, so Docker builds
  without WASM build args correctly fall through to hardcoded CDN defaults
- Show CDN defaults as placeholder text in WASM settings page instead of
  filling input values, with "Pre-configured" status badge
- Fix nginx redirecting locale URLs without trailing slash (e.g. /de) to
  internal port 8080 by adding absolute_redirect off
- Handle encrypted PDF error in compress tool with descriptive message
- Replace Docker Hub pulls badge with GHCR downloads badge

nginx.conf

@@ -25,7 +25,8 @@ http {
         server_name localhost;
         root /usr/share/nginx/html;
         index index.html;
-        
+        absolute_redirect off;
+
 
         location ~* \.html$ {
             expires 1h;