8 diagnostic checks: Python version (3.10+), package install, git,
14 core deps, 10 optional deps, API keys, MCP server, output dir.
Each check reports pass/warn/fail with --verbose for extra detail.
Exit code 0 if no critical failures, 1 otherwise.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
