bbb: WIP—stabilize env/compose wiring & prep SFU override

Context: debugging mediasoup/WebRTC failures caused by empty/interpolated vars (EXTERNAL_IPv4, etc.).
- Normalize config/main.yml (ip6_enabled flag, enable greenlight/coturn) and tidy formatting.
- Extend vars/main.yml with BBB_* switches (IPv6, Greenlight, Coturn), TURN/Coturn cert paths.
- env.j2: wire secrets & toggles, guard IPv6 via BBB_IP6_ENABLED, switch LDAP/OIDC to role flags, add TURN/STUN, and general cleanup.
- tasks/main.yml: use BBB_* fact names, robust path joins, write docker-compose.override.yml, and notify compose on env/override changes.
- tasks/01_docker-compose.yml: reference new BBB_DOCKER_COMPOSE_* facts.
- Add templates/docker-compose.override.yml.j2 (placeholder for SFU overrides to avoid bad defaults during runs).
Rationale: make Compose brings deterministic (no empty ), paving the way to set MS_WEBRTC_LISTEN_IPS in override without risk.

Chat reference: debugging thread with GPT-5 Thinking on 2025-09-26 https://chatgpt.com/share/68d59d98-4388-800f-a627-07b6a603d0b2.

roles/web-app-bigbluebutton/config/main.yml

@@ -1,15 +1,14 @@
-enable_greenlight:    "true"
-api_suffix:           "/bigbluebutton/"
+api_suffix:             "/bigbluebutton/"
 features:
-  matomo:             true
-  css:                true
-  desktop:            false # Videos can't open in frame due to iframe restrictions
-                            # @todo fix this
-  ldap:               false
-  oidc:               true
-  central_database:   false # Propably required for backup routines
-  logout:             true
+  matomo:               true
+  css:                  true
+  desktop:              false # Videos can't open in frame due to iframe restrictions
+  ldap:                 false
+  oidc:                 true
+  central_database:     false # Propably required for backup routines
+  logout:               true
 server:
+  ip6_enabled:          false
   csp:
     flags:
       script-src-elem:
@@ -29,4 +28,8 @@ docker:
       version:    "main"  
     database:
       # This is set to true to pass integration test, doesn't have any other function
-      enabled: true
+      enabled:    true
+    greenlight:
+      enabled:    true
+    coturn:
+      enabled:    true