feat: built-in ssh-mcp healthcheck CLI + Dockerfile integration (v0.5.4)

[blackaxgit]

Summary

New ssh-mcp healthcheck CLI subcommand implemented by 3 parallel agents. Replaces the ~40-line inline Python healthcheck that operators previously had to embed in their compose files.

Agent	Files	Delivered
healthcheck-core	healthcheck.py, server.py, test_healthcheck.py	New module, CLI dispatch, 13 tests
docker-integration	Dockerfile, compose.yaml	Baked-in HEALTHCHECK, simplified compose
docs-version	README, CHANGELOG, init.py	New docs section, v0.5.4 bump

What it does

• Auto-detects transport via SSH_MCP_TRANSPORT
• stdio mode: import check + config parse
• http mode: real MCP initialize JSON-RPC POST
• Auth modes: reads SSH_MCP_HTTP_TOKEN / SSH_MCP_HTTP_TOKEN_FILE, respects SSH_MCP_HTTP_AUTH=none
• 4xx responses = healthy (server alive, request rejected)
• 5xx / URLError = unhealthy
• Stdlib only — no curl/wget dependency
• 3-second hard timeout
• Never logs the token

Quality gates

Check	Result
pytest	520 passed (+13 new)
mypy strict	clean (7 files)
ruff check	clean
ruff format	clean

Operator UX win

Before:

healthcheck:
  test:
    - CMD-SHELL
    - |
      python3 -c "
      import json, os, sys, urllib.request
      port = os.environ.get('SSH_MCP_HTTP_PORT', '8000')
      # ... 30 more lines ...
      "

After:

(nothing — Dockerfile HEALTHCHECK handles it)