refactor: adopt nginx configuration templates

Use Nginx templates for environment-based configuration generation and update example.env.

nginx/compose.yaml

@@ -4,9 +4,11 @@ services:
     image: nginx:1-alpine
     container_name: nginx
     volumes:
-      - /srv/data/nginx/conf.d:/etc/nginx/conf.d:ro
+      - /srv/data/nginx/templates:/etc/nginx/templates:ro
       - /srv/data/nginx/snippets:/etc/nginx/snippets:ro
       - /srv/data/nginx/certs:/etc/nginx/certs:ro
+    environment:
+      BASE_DOMAIN: ${BASE_DOMAIN}
     ports:
       - "192.168.10.101:80:80"
       - "192.168.10.101:443:443"