Nextcloud: integrate Talk & Whiteboard; adjust ports & healthchecks

- Enable Spreed (Talk); signaling via /standalone-signaling/
- STUN/TURN: move STUN to 3480 (3479 occupied by BBB), keep TURN 5350 reserved
- docker-compose: expose internal WS ports; explicit TURN port mapping
- Healthchecks: add nc-based TCP checks (roles/docker-container/templates/healthcheck/nc.yml.j2)
- Nginx: location proxy to talk:8081
- Schema: add talk_* secrets (turn/signaling/internal)
- Plugins: configure spreed/whiteboard via vars/*; remove old task files
- Ports matrix (group_vars/all/09_ports.yml) updated/commented

Conversation: https://chatgpt.com/share/68b61a6a-e1dc-800f-b793-4aa600bc0166

roles/web-app-nextcloud/templates/nginx/docker.conf.j2

@@ -189,5 +189,14 @@ http {
             proxy_set_header   Connection        "upgrade";
             proxy_read_timeout 3600;
         }
+
+        location {{ NEXTCLOUD_TALK_LOCATION }} {
+            proxy_pass         http://talk:{{ NEXTCLOUD_TALK_INTERNAL_PORT }}/;
+            proxy_http_version 1.1;
+            proxy_set_header   Host              $host;
+            proxy_set_header   Upgrade           $http_upgrade;
+            proxy_set_header   Connection        "upgrade";
+            proxy_read_timeout 3600;
+        }
     }
 }