feat: Add support for OpenRouter as an LLM provider.

[elskito]

Summary

OpenRouter API support added to app

PR contains:

• modified README
• modified code for OpenRouter compatibility
• modified config for OpenRouter compatibility

[vas3k]

I've never heard of such a platform, to be honest. It looks like an aggregator that, in theory, gives access to many LLMs at once, which is useful for sure. But I'm doubting the need to include it in the standard deployment. Only models that work good with images (webp, to be precise) are suitable for TaxHacker, so I would rather add proven LLMs to avoid confusing users and leaving them with a non-functional application.

For example, I would be happy if one of the DeepSeek and Ollama models were a separate option for self-hosted users

[adryserage]

Code Review Analysis 🔍

Thanks for adding OpenRouter support! This is a clean implementation. Here are some suggestions:

✅ What looks good

• Clean integration following existing provider patterns
• Proper environment variable setup in .env.example
• Good use of the existing ChatOpenAI class with custom baseURL

💡 Suggestions for improvement

1. Model name inconsistency: The default model in .env.example is openai/gpt-4.1-mini but in lib/llm-providers.ts it's openai/gpt-4.1-mini and in forms/settings.ts it's openai/gpt-4o-mini. Consider standardizing to openai/gpt-4o-mini which is the correct OpenAI model ID format.

2. Consider adding model suggestions: Similar to other providers, you might want to add a suggestedModels array to help users know which models are available on OpenRouter:
   ```typescript
   suggestedModels: ["openai/gpt-4o-mini", "anthropic/claude-3-haiku", "google/gemini-flash-1.5"]
   ```

3. Error handling: OpenRouter may return different error formats than OpenAI. Consider adding specific error handling for OpenRouter responses.

🔗 Related

Note: I've opened PR #58 and #59 which improve error messages for invalid models and add dynamic model fetching from provider APIs. These changes would complement your OpenRouter addition well!

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Automated review by Aetheris