feat(filters): enforce safe Node.js heap sizing via reusable filter

- Add node_autosize filter (node_max_old_space_size) using get_app_conf
- Raise error when mem_limit < min_mb to prevent OOM-kill misconfigurations
- Wire Whiteboard NODE_OPTIONS and increase mem_limit to 1g; set cpus=1
- Refactor PeerTube to use the same filter; simplify vars
- Add unit tests; keep integration filters usage green

Context: https://chatgpt.com/share/690e0499-6a94-800f-b8ed-2c5124690103

roles/web-app-nextcloud/templates/docker-compose.yml.j2

@@ -77,7 +77,8 @@
     volumes:
       - whiteboard_tmp:/tmp
       - whiteboard_fontcache:/var/cache/fontconfig
-
+    environment:
+      - NODE_OPTIONS=--max-old-space-size={{ NEXTCLOUD_WHITEBOARD_MAX_OLD_SPACE_SIZE }}
     expose:
       - "{{ container_port }}"
     shm_size: 1g