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/config/main.yml

@@ -93,9 +93,9 @@ docker:
       version:              "latest"
       backup:
         no_stop_required:   true
-      cpus:                 "0.25"
+      cpus:                 "1"
       mem_reservation:      "128m"
-      mem_limit:            "512m"
+      mem_limit:            "1g"
       pids_limit:           1024
   enabled:  "{{ applications | get_app_conf('web-app-nextcloud', 'features.oidc', False, True, True) }}"   # Activate OIDC for Nextcloud
   # floavor decides which OICD plugin should be used.