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/config/main.yml

@@ -74,9 +74,9 @@ docker:
       backup:
         no_stop_required:   false
       turn_server:
-        onboard_enabled:    true # Deactivated because standalone turnserver works with  Big Blue Button, so I assume that the nextcloud internal turnserver has it's isssues
+        onboard_enabled:    true
         standalone_enabled: false
-      network_mode:         host
+      network_mode:         bridge
       cpus:                 "1.0"
       mem_reservation:      "256m"
       mem_limit:            "1g"