Add OpenRouter support as LLM provider

Description

Add support for OpenRouter as an LLM provider to enable access to multiple models through a single API.

Files to Look At

Provider Implementation

• apps/webapp/app/lib/batch/providers/anthropic.ts - Reference for provider structure
• apps/webapp/app/lib/batch/providers/openai.ts - Another provider example

Configuration

• docs/providers/ - Provider documentation directory
• docs/self-hosting/environment-variables.mdx - Where to add new env vars

Implementation Tasks

• Create apps/webapp/app/lib/batch/providers/openrouter.ts
• Add OpenRouter API integration
• Add environment variable configuration (OPENROUTER_API_KEY)
• Create documentation in docs/providers/openrouter.mdx
• Update environment variables documentation
• Add model selection UI if needed

Technical Notes

1. OpenRouter uses an OpenAI-compatible API, so you can likely extend/adapt the OpenAI provider
2. API endpoint: https://openrouter.ai/api/v1
3. Requires HTTP-Referer and X-Title headers for attribution
4. Supports streaming responses

Resources

• OpenRouter API Docs

Labels

good first issue, enhancement