feat(coturn): add dedicated web-svc-coturn role with schema, ports, network, and docker-compose template

- registered subnet 192.168.104.48/28 for coturn in group_vars/all/09_networks.yml
- defined public ports for stun/turn and relay port range in group_vars/all/10_ports.yml
- removed obsolete TODO.md and env.j2 from role
- added schema/main.yml with credentials validation (user_password, auth_secret)
- refactored tasks to load sys-stk-back-stateless instead of sys-stk-full-stateful
- implemented docker-compose.yml.j2 with auth-secret + lt-cred-mech and TLS config
- restructured vars/main.yml with docker, ports, credentials, and certificates
- updated config/main.yml.j2 with canonical domain and service definitions

Conversation: https://chatgpt.com/share/68d6c4a8-d524-800f-9592-e8a3407cd721

roles/web-svc-coturn/schema/main.yml

@@ -0,0 +1,9 @@
+credentials:
+  user_password:
+    description:  "Long-Term Credential password for clients"
+    algorithm:    "alphanumeric_32"
+    validation:   "^[A-Za-z0-9]{32}$"
+  auth_secret:
+    description:  "TURN-REST static auth secret"
+    algorithm:    "sha1"
+    validation:   "^[a-f0-9]{40}$"