fix(nginx): use resolver and variable proxy_pass for dynamic DNS

Nginx crashes on startup if upstream hostnames (api.anyplot.ai) cannot
be resolved. Use Google DNS resolver and set variables for proxy_pass
so nginx resolves at request time instead of startup.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: MarkusNeusinger

app/nginx.conf

@@ -34,6 +34,10 @@ server {
     listen 8080;
     server_name _;
 
+    # Use Google DNS for dynamic upstream resolution (prevents startup crash when domain not yet in DNS)
+    resolver 8.8.8.8 8.8.4.4 valid=300s;
+    resolver_timeout 5s;
+
     # Root directory for serving files
     root /usr/share/nginx/html;
     index index.html;
@@ -60,7 +64,8 @@ server {
 
     # Named location for bot SEO proxy
     location @seo_proxy {
-        proxy_pass https://api.anyplot.ai/seo-proxy$request_uri;
+        set $seo_backend https://api.anyplot.ai;
+        proxy_pass $seo_backend/seo-proxy$request_uri;
         proxy_set_header Host api.anyplot.ai;
         proxy_ssl_server_name on;
         proxy_ssl_verify on;
@@ -92,7 +97,8 @@ server {
 
     # Proxy sitemap.xml to backend API (dynamic generation)
     location = /sitemap.xml {
-        proxy_pass https://api.anyplot.ai/sitemap.xml;
+        set $sitemap_backend https://api.anyplot.ai;
+        proxy_pass $sitemap_backend/sitemap.xml;
         proxy_set_header Host api.anyplot.ai;
         proxy_ssl_server_name on;
     }