List provider backends and their auth status

Usage: hephaes providers [OPTIONS]

Options:
      --provider <PROVIDER>        Model provider backend to use for this run [possible values:
                                   claude, codex, anthropic, openai, openrouter, ollama]
      --model <MODEL>              Model id (provider-specific). Omit to use the provider/CLI
                                   default
      --wiki-dir <WIKI_DIR>        Wiki output directory (default: ./wiki)
      --concurrency <CONCURRENCY>  Max concurrent page builds (reserved; sequential in v1)
  -v, --verbose                    Show every tool call as the agent works
  -q, --quiet                      Suppress progress output; print only the final summary
  -h, --help                       Print help
