feat: add gitea workflows for kubeadm bootstrap and reset

nixos/kubeadm/README.md

@@ -115,6 +115,20 @@ For a full nuke/recreate lifecycle:
 - run Terraform destroy/apply for VMs first,
 - then run `./scripts/rebuild-and-bootstrap.sh` again.
 
+## Optional Gitea workflow automation
+
+Manual dispatch workflows are available:
+
+- `.gitea/workflows/kubeadm-bootstrap.yml`
+- `.gitea/workflows/kubeadm-reset.yml`
+
+Required repository secrets:
+
+- `KUBEADM_SSH_PRIVATE_KEY`
+- `KUBEADM_SSH_USER`
+- `KUBEADM_CP_1_IP`, `KUBEADM_CP_2_IP`, `KUBEADM_CP_3_IP`
+- `KUBEADM_WK_1_IP`, `KUBEADM_WK_2_IP`, `KUBEADM_WK_3_IP`
+
 ## Notes
 
 - Scripts are intentionally manual-triggered (predictable for homelab bring-up).