Revert hostname to localhost, drop proxy-headers config

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

docker-compose.yml

@@ -27,9 +27,8 @@ services:
       KC_DB_URL: jdbc:postgresql://postgres:5432/keycloak
       KC_DB_USERNAME: keycloak
       KC_DB_PASSWORD: keycloak
-      KC_HOSTNAME: https://auth.e-cosplay.fr
+      KC_HOSTNAME: localhost
       KC_HTTP_ENABLED: "true"
-      KC_PROXY_HEADERS: xforwarded
       KC_HEALTH_ENABLED: "true"
       KC_METRICS_ENABLED: "true"
       KEYCLOAK_ADMIN: admin