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/docker.conf.j2

@@ -39,7 +39,7 @@ http {
     #gzip  on;
 
     upstream php-handler {
-        server application:9000;
+        server {{ NEXTCLOUD_SERVICE }}:9000;
     }
 
     server {
@@ -192,12 +192,12 @@ http {
             proxy_read_timeout 3600;
         }
 
-{% if NEXTCLOUD_TALK_SIGNALING_ENABLED | bool %}
-        location {{ NEXTCLOUD_TALK_SIGNALING_LOCATION }} {
-{% if NEXTCLOUD_TALK_NETWORK_MODE == 'host' %}
-            proxy_pass          http://host.docker.internal:{{ NEXTCLOUD_TALK_SIGNALING_PORT }}/;
+{% if NEXTCLOUD_HPB_SIGNALING_ENABLED | bool %}
+        location {{ NEXTCLOUD_HPB_SIGNALING_LOCATION }} {
+{% if NEXTCLOUD_HPB_NETWORK_MODE == 'host' %}
+            proxy_pass          http://host.docker.internal:{{ NEXTCLOUD_HPB_SIGNALING_PORT }}/;
 {% else %}
-            proxy_pass          http://talk:{{ NEXTCLOUD_TALK_SIGNALING_PORT }}/;
+            proxy_pass          http://talk:{{ NEXTCLOUD_HPB_SIGNALING_PORT }}/;
 {% endif %}
             proxy_http_version  1.1;
             proxy_set_header    Host              $host;