feat(ipa): add AuthorizedKeysCommand + enroll tailscale-router

- modules/ipa/client.nix: add AuthorizedKeysCommand so sshd fetches SSH
  public keys from IPA via sss_ssh_authorizedkeys, enabling pubkey login
  without per-host authorized_keys files

- hosts/tailscale-router/host.nix: add IPA client module + networking.domain
  so SSSD runs and wayne can authenticate on this host

- secrets/tailscale-router.keytab: sops-encrypted keytab for
  tailscale-router.sweet.home (generated by create-nixos-ipa-host-account.sh)

- .sops.yaml: creation rule for secrets/tailscale-router.keytab

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.sops.yaml

@@ -127,6 +127,16 @@ creation_rules:
   # scripts/secrets/sync-host-keys.sh yet, so whichever variant is actually
   # deployed next needs its recipient added here (and `sops updatekeys` rerun)
   # before it can decrypt this.
+  # Host keytab for tailscale-router FreeIPA enrollment (binary sops file).
+  # Generated by scripts/ipa/create-nixos-ipa-host-account.sh.
+  - path_regex: secrets/tailscale-router\.keytab$
+    key_groups:
+      - age:
+          - *admin
+          - *lxc-tailscale-router
+          - *proxmox-tailscale-router
+          - *linode-tailscale-router
+
   - path_regex: secrets/gui\.yaml$
     key_groups:
       - age: