Fix nginx template to use correct path for third_party assets

- Changed alias from ${NIXPACKS_PHP_ROOT_DIR}/pancake/third_party to /app/pancake/third_party
- This fixes 404 errors for JS/CSS files with query strings
- NIXPACKS_PHP_ROOT_DIR variable not being set properly in containers
- Static assets now serve correctly from all containers

nginx.template.conf

@@ -82,7 +82,7 @@ http {
 
         # Static assets for pancake/third_party
         location /pancake/third_party {
-            alias ${NIXPACKS_PHP_ROOT_DIR}/pancake/third_party;
+            alias /app/pancake/third_party;
             expires 1y;
             add_header Cache-Control "public, immutable";