chore: Externalize sensitive credentials in docker-compose.yml to environment variables and add .env to .gitignore.

.gitignore

@@ -1,2 +1,3 @@
 node_modules/
 client/config.json
+.env

docker-compose.yml

@@ -7,9 +7,9 @@ services:
       - "3000:3000"
     restart: always
     environment:
-      - BROADCASTER_PASSWORD=MySuperSecurePassword123
-      - TURN_USER=myuser
-      - TURN_PASSWORD=mypassword
+      - BROADCASTER_PASSWORD=${BROADCASTER_PASSWORD}
+      - TURN_USER=${TURN_USER}
+      - TURN_PASSWORD=${TURN_PASSWORD}
 
   coturn:
     image: coturn/coturn:latest
@@ -21,5 +21,5 @@ services:
       --min-port=49152
       --max-port=49252
       --realm=yourdomain.com
-      --user=myuser:mypassword
+      --user=${TURN_USER}:${TURN_PASSWORD}
       --stale-nonce