[WIP] feat: add multi-provider support feature specification

[stay-foolish-forever]

Description

OpenCodeReview currently supports two main LLM API protocols:

• Anthropic Messages API
• OpenAI Chat Completions API

While this covers major providers like Anthropic Claude, OpenAI, and Azure OpenAI, there's a growing ecosystem of LLM providers with their own APIs or OpenAI-compatible endpoints. This feature aims to:

1. Support more LLM providers - Enable integration with providers like:

   • Google Gemini
   • Alibaba Qwen (通义千问)
   • Baidu ERNIE (文心一言)
   • Zhipu AI GLM
   • DeepSeek
   • Other OpenAI-compatible endpoints

2. Simplify configuration - Provide a unified configuration interface for different providers

3. Enable provider-specific optimizations - Allow provider-specific features like:

   • Custom authentication methods
   • Provider-specific parameters
   • Optimized request/response handling
   • Cost tracking per provider

Type of Change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Refactoring (no functional changes)
• Documentation update
• CI / Build / Tooling

How Has This Been Tested?

• make test passes locally
• Manual testing (describe below)

Checklist

• My code follows the project's coding style (go fmt, go vet)
• I have performed a self-review of my code
• I have added tests that prove my fix is effective or my feature works
• New and existing unit tests pass locally with my changes
• I have updated the documentation accordingly (if applicable)
• I have signed the CLA

Related Issues

[stay-foolish-forever]

/open-code-review

[github-actions]

✅ OpenCodeReview: No supported files changed.