feat: Add SSH remote execution for HAProxy on remote host

MCP server can now manage HAProxy running on a remote host via SSH.
When SSH_HOST env var is set, all file I/O and subprocess commands
(podman, acme.sh, openssl) are routed through SSH instead of local exec.

- Add ssh_ops.py module with remote_exec, run_command, file I/O helpers
- Modify file_ops.py to support remote reads/writes via SSH
- Update all tools (domains, certificates, health, configuration) for SSH
- Fix domains.py: replace direct fcntl usage with file_lock context manager
- Add openssh-client to Docker image for SSH connectivity
- Update k8s deployment with SSH env vars and SSH key secret mount

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

k8s/deployment.yaml

@@ -32,8 +32,20 @@ spec:
               value: "10.253.100.107"
             - name: HAPROXY_PORT
               value: "9999"
+            - name: SSH_HOST
+              value: "10.253.100.107"
+            - name: SSH_USER
+              value: "root"
+            - name: SSH_KEY
+              value: "/root/.ssh/id_rsa"
+            - name: SSH_PORT
+              value: "22"
             - name: LOG_LEVEL
               value: "INFO"
+          volumeMounts:
+            - name: ssh-key
+              mountPath: /root/.ssh
+              readOnly: true
           readinessProbe:
             tcpSocket:
               port: 8000
@@ -51,3 +63,8 @@ spec:
             limits:
               memory: "256Mi"
               cpu: "500m"
+      volumes:
+        - name: ssh-key
+          secret:
+            secretName: haproxy-ssh-key
+            defaultMode: 0600