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>

haproxy_mcp/tools/health.py

@@ -1,7 +1,6 @@
 """Health check tools for HAProxy MCP Server."""
 
 import json
-import os
 import subprocess
 import time
 from typing import Annotated, Any
@@ -18,6 +17,8 @@ from ..validation import validate_domain, validate_backend_name
 from ..haproxy_client import haproxy_cmd
 from ..file_ops import get_backend_and_prefix
 from ..utils import parse_stat_csv, parse_servers_state
+from ..ssh_ops import run_command, remote_file_exists
+from ..config import REMOTE_MODE
 
 
 def register_health_tools(mcp):
@@ -65,9 +66,9 @@ def register_health_tools(mcp):
 
         # Check container status
         try:
-            container_result = subprocess.run(
+            container_result = run_command(
                 ["podman", "inspect", "--format", "{{.State.Status}}", HAPROXY_CONTAINER],
-                capture_output=True, text=True, timeout=5
+                timeout=5,
             )
             if container_result.returncode == 0:
                 container_status = container_result.stdout.strip()
@@ -88,7 +89,8 @@ def register_health_tools(mcp):
         files_ok = True
         file_status: dict[str, str] = {}
         for name, path in [("map_file", MAP_FILE), ("servers_file", SERVERS_FILE)]:
-            if os.path.exists(path):
+            exists = remote_file_exists(path) if REMOTE_MODE else __import__('os').path.exists(path)
+            if exists:
                 file_status[name] = "ok"
             else:
                 file_status[name] = "missing"