Evolve DNS Challenge to DNS-PERSIST-01

[nicgen]

Let's Encrypt has introduced the DNS-PERSIST-01 challenge (SC-088v3).

Goal: Switch from standard DNS-01 to DNS-PERSIST-01 to avoid frequent TXT record updates.

Steps:

1. Verify Traefik support.
2. Create persistent TXT record in Cloudflare.
3. Update Traefik config.

Reference: https://letsencrypt.org/2026/02/18/dns-persist-01