feat(provider): support OfoxAI as system provider

[Gtr206]

OfoxAI (https://ofox.ai) is a unified LLM API gateway that provides access to 100+ models — including OpenAI, Anthropic, Google Gemini, Meta Llama, DeepSeek, Qwen, Mistral, and more — through a single API key. It is wire-compatible with the OpenAI, Anthropic, and Gemini protocols, so users can switch between models with one credential.

Adding OfoxAI as a system provider gives Cherry Studio users another option for centralized model access alongside AiHubMix, OpenRouter, etc.

What this PR adds

• types/provider.ts: register 'ofoxai' in SystemProviderIdSchema and SystemProviderIds.
• config/providers.ts:
  • logo import (ofoxai.png)
  • SYSTEM_PROVIDERS_CONFIG entry — type openai, apiHost: https://api.ofox.ai/v1, anthropicApiHost: https://api.ofox.ai/anthropic
  • PROVIDER_LOGO_MAP entry
  • PROVIDER_URLS entry pointing at https://ofox.ai, https://app.ofox.ai, and https://docs.ofox.ai
• config/models/default.ts: 10 representative predefined models (GPT-4o family, Claude Sonnet, Gemini 2.5, DeepSeek V3/R1, Qwen-coder). Users can add any other OfoxAI model manually.
• assets/images/providers/ofoxai.png: provider logo.

Notes for reviewers

• The provider is enabled: false by default — users have to explicitly enable it and enter their API key, same as every other system provider.
• Both OpenAI and Anthropic protocol endpoints are wired up (apiHost and anthropicApiHost), so Claude prompt-caching support can be added later by including 'ofoxai' in isSupportAnthropicPromptCacheProvider. Left out of this PR to keep it minimal — happy to follow up if maintainers want it included.