feat: lock Forgejo install wizard via env var

Sets FORGEJO__security__INSTALL_LOCK=true so Forgejo skips the first-run
wizard and uses the env var configuration directly.

https://claude.ai/code/session_01FKCW3FDjNFj6jve4niMFXH

infra/docker-compose.yml

@@ -91,6 +91,8 @@ services:
       FORGEJO__server__DOMAIN: ${FORGEJO_DOMAIN}
       FORGEJO__server__ROOT_URL: https://${FORGEJO_DOMAIN}/
       FORGEJO__server__SSH_DOMAIN: ${FORGEJO_DOMAIN}
+      # Skip the first-run wizard — everything is configured via env vars above.
+      FORGEJO__security__INSTALL_LOCK: "true"
     volumes:
       - forgejo-data:/data
     depends_on: