net/traefik: Update to upstream release 3.7.1
Details:
- Update to 3.7.x branch, details see: https://github.com/traefik/traefik/releases/tag/v3.7.1
- Breaking changes are not expected, but double-checking the migration guide is still recommended: https://doc.traefik.io/traefik/v3.7/migrate/v3/#v371
MFH: 2026Q2
Security: CVE-2026-44774