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>

Dockerfile

@@ -12,6 +12,8 @@ COPY haproxy_mcp/ ./haproxy_mcp/
 
 FROM python:3.11-slim
 
+RUN apt-get update && apt-get install -y --no-install-recommends openssh-client && rm -rf /var/lib/apt/lists/*
+
 WORKDIR /app
 
 COPY --from=builder /usr/local/lib/python3.11/site-packages /usr/local/lib/python3.11/site-packages