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/schema/main.yml

@@ -6,4 +6,16 @@ credentials:
   administrator_password:
     description: "Initial password for the Nextcloud administrator (change immediately and enable 2FA)"
     algorithm: "sha256"
-    validation: "^[a-f0-9]{64}$"
+    validation: "^[a-f0-9]{64}$"
+  talk_turn_secret:
+    description: "TURN REST secret for coturn"
+    algorithm: "base64_prefixed_32"
+    validation: "^base64:[A-Za-z0-9+/]{43}=$"
+  talk_signaling_secret:
+    description: "Secret for Talk signaling"
+    algorithm: "base64_prefixed_32"
+    validation: "^base64:[A-Za-z0-9+/]{43}=$"
+  talk_internal_secret:
+    description: "Internal secret for AIO Talk"
+    algorithm: "base64_prefixed_32"
+    validation: "^base64:[A-Za-z0-9+/]{43}=$"