feat(cli): add custom provider setup in init wizard

[mfzzf]

Summary

This PR adds support for configuring a custom OpenAI-compatible provider in the TUI init wizard.

Key updates

• Add Custom as a selectable provider in Step 3 of 8
• Introduce a new Step 4 of 8 to configure:
  • Provider name
  • API key env var (auto-derived, editable)
  • Base URL
  • Default model
• Reuse configured custom values in subsequent steps:
  • API key input prompt (Step 5 of 8) shows provider + env var
  • Model selection uses the custom model as default

Validation

• Provider name and model cannot be empty
• base_url must start with http:// or https://

---

UX (Final Style)

Step 3 of 8

OpenFang Init  3 of 8
────────────────────────────────────────────────────────────
  Choose your LLM provider:

▸   Groq          requires GROQ_API_KEY (free tier)
    Gemini        requires GEMINI_API_KEY (free tier)
    DeepSeek      requires DEEPSEEK_API_KEY (cheap)
    Anthropic     requires ANTHROPIC_API_KEY
    OpenAI        requires OPENAI_API_KEY
    OpenRouter    requires OPENROUTER_API_KEY
    Together      requires TOGETHER_API_KEY
    Mistral       requires MISTRAL_API_KEY
    Fireworks     requires FIREWORKS_API_KEY
○ Ollama        local, no key needed
○ LM Studio     local, no key needed
○ Custom        local, no key needed

Step 4 of 8

OpenFang Init  4 of 8
────────────────────────────────────────────────────────────
  Configure custom OpenAI-compatible provider:

  Provider: custom-openai
  API env:  CUSTOM_OPENAI_API_KEY  (API key entered next step)
  Base URL: http://localhost:8000/v1
  Model:    gpt-5.2
  Example base_url: http://localhost:8000/v1

Step 5 of 8

OpenFang Init  5 of 8
────────────────────────────────────────────────────────────
  Enter your Custom (custom-openai) API key:

  ▸ •••••••••••••••█

    Or set CUSTOM_OPENAI_API_KEY environment variable

---

Why

Users running self-hosted or third-party OpenAI-compatible endpoints need first-class setup support in openfang init without hacking provider defaults or env names manually.

---

Testing

• Select Custom in provider list and verify navigation to Step 4
• Verify field editing for provider/env/base_url/model
• Validate empty provider/model error handling
• Validate base URL scheme check (http:// / https://)
• Verify Step 5 API key prompt reflects custom provider/env var

[mfzzf]

@jaberjaber23 Hi! I’ve implemented first-class Custom Provider support in openfang init in this PR #50. When you have a moment, could you please take a look? Would really appreciate your feedback 🙏

[OptionalCoin]

Hope this is implemented because many of use use CLIProxyAPI/OmniRouter.

[Chivier]

Hope this is implemented because many of use use CLIProxyAPI/OmniRouter.

Agree, this feature is essential