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/haproxy_client.py

@@ -1,7 +1,6 @@
 """HAProxy Runtime API client functions."""
 
 import socket
-import subprocess
 import select
 import time
 
@@ -14,6 +13,7 @@ from .config import (
     SUBPROCESS_TIMEOUT,
 )
 from .exceptions import HaproxyError
+from .ssh_ops import run_command
 
 
 def haproxy_cmd(command: str) -> str:
@@ -147,23 +147,23 @@ def reload_haproxy() -> tuple[bool, str]:
         Tuple of (success, message)
     """
     try:
-        validate = subprocess.run(
+        validate = run_command(
             ["podman", "exec", HAPROXY_CONTAINER, "haproxy", "-c", "-f", "/usr/local/etc/haproxy/haproxy.cfg"],
-            capture_output=True, text=True, timeout=SUBPROCESS_TIMEOUT
+            timeout=SUBPROCESS_TIMEOUT,
         )
         if validate.returncode != 0:
             return False, f"Config validation failed:\n{validate.stderr}"
 
-        result = subprocess.run(
+        result = run_command(
             ["podman", "kill", "--signal", "USR2", HAPROXY_CONTAINER],
-            capture_output=True, text=True, timeout=SUBPROCESS_TIMEOUT
+            timeout=SUBPROCESS_TIMEOUT,
         )
         if result.returncode != 0:
             return False, f"Reload failed: {result.stderr}"
         return True, "OK"
-    except subprocess.TimeoutExpired:
+    except TimeoutError:
         return False, f"Command timed out after {SUBPROCESS_TIMEOUT} seconds"
     except FileNotFoundError:
-        return False, "podman command not found"
+        return False, "ssh/podman command not found"
     except OSError as e:
         return False, f"OS error: {e}"