refactor(dns): unify Cloudflare + Hetzner handling across roles

- replaced CERTBOT_DNS_API_TOKEN with CLOUDFLARE_API_TOKEN everywhere
- introduced generic sys-dns-cloudflare-records role for managing DNS records
- added sys-dns-hetzner-rdns role with both Cloud (hcloud) and Robot API flavors
- updated Mailu role to:
  - generate DKIM before DNS setup
  - delegate DNS + rDNS records to the new generic roles
- removed legacy per-role Cloudflare vars (MAILU_CLOUDFLARE_API_TOKEN)
- extended group vars with HOSTING_PROVIDER for rDNS flavor decision
- added hetzner.hcloud collection to requirements

This consolidates DNS management into reusable roles,
supports both Cloudflare and Hetzner providers,
and standardizes variable naming across the project.

roles/sys-dns-hetzner-rdns/meta/main.yml

@@ -0,0 +1,24 @@
+
+---
+galaxy_info:
+  author: "Kevin Veen-Birkenbach"
+  description: "Generic role to manage reverse DNS (PTR) for Hetzner Cloud resources (server, primary_ip, floating_ip, load_balancer)."
+  license: "Infinito.Nexus NonCommercial License"
+  license_url: "https://s.infinito.nexus/license"
+  company: |
+    Kevin Veen-Birkenbach
+    Consulting & Coaching Solutions
+    https://www.veen.world
+  galaxy_tags:
+    - hetzner
+    - dns
+    - rdns
+    - ptr
+    - mail
+  repository: "https://s.infinito.nexus/code"
+  issue_tracker_url: "https://s.infinito.nexus/issues"
+  documentation: "https://docs.infinito.nexus"
+  logo:
+    class: "fa-solid fa-server"
+  run_after: []
+dependencies: []