Simplify nginx template by removing conditional root block

- Removed if(NIXPACKS_PHP_ROOT_DIR) conditional block
- Set root directly to /app since NIXPACKS_PHP_ROOT_DIR variable not set
- This fixes nginx config issues and simplifies template
- Ensures consistent behavior across all deployments

nginx.template.conf

@@ -29,11 +29,7 @@ http {
         listen [::]:${PORT};
         server_name localhost;
 
-        $if(NIXPACKS_PHP_ROOT_DIR) (
-            root ${NIXPACKS_PHP_ROOT_DIR};
-        ) else (
         root /app;
-        )
         # Block access to hidden files and directories
         location ~ /\. {
             deny all;