Nextcloud: refactor Talk → HPB, switch to bridge mode, and template cleanups

- Change Talk (HPB) network_mode from host → bridge and drop TURN relay range mapping
- Remove obsolete nginx restart handler; rely on 'docker compose up' notify
- Fix spreed task condition to use HPB standalone flag
- docker-compose.yml.j2: parameterize service names, use NEXTCLOUD_*_SERVICE vars, align host-gateway condition with HPB, tidy ports/expose/network blocks
- env.j2/nginx configs: rename TALK_* → HPB_* variables and locations; use templated NEXTCLOUD_SERVICE for php upstream
- vars: introduce entity_name; centralize *SERVICE keys; rename all Talk vars to HPB; adjust whiteboard keys; compute URLs/JSON configs accordingly
- spreed plugin vars: point to HPB signaling/STUN/TURN and internal secret

Ref: https://chatgpt.com/share/68db9f41-16ec-800f-9cdf-7530862f89aa

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

@@ -17,8 +17,8 @@ server
   client_body_buffer_size 400M;
   fastcgi_buffers 64 4K;
 
-  {% if NEXTCLOUD_TALK_SIGNALING_ENABLED | bool %}
-    {% set location_ws = '^~ ' ~ NEXTCLOUD_TALK_SIGNALING_LOCATION %}
+  {% if NEXTCLOUD_HPB_SIGNALING_ENABLED | bool %}
+    {% set location_ws = '^~ ' ~ NEXTCLOUD_HPB_SIGNALING_LOCATION %}
     {% set ws_port     = NEXTCLOUD_PORT %}
     {% include 'roles/sys-svc-proxy/templates/location/ws.conf.j2' %}
   {% endif %}