feat(providers): support custom base_url for Anthropic provider

[aw338WoWmUI]

Summary

Enable configuring third-party Anthropic-compatible API endpoints (e.g., MiniMax, OpenRouter) through the base_url configuration option.

Changes

g3-providers/src/anthropic.rs

• Add base_url field to AnthropicProvider struct
• Refactor new() to delegate to new_with_name() to reduce code duplication
• Add base_url parameter to new_with_name() with default to official Anthropic API URL
• Update create_request_builder() to use self.base_url instead of hardcoded URL

g3-config/src/lib.rs

• Add base_url: Option<String> field to AnthropicConfig

g3-core/src/provider_registration.rs

• Pass base_url from config when registering Anthropic providers

g3-planner/src/llm.rs

• Pass base_url when creating planner Anthropic provider

g3-providers/src/lib.rs

• Add PartialEq derive to MessageRole (required for testing)

Motivation

Some providers like MiniMax offer Anthropic-compatible API endpoints. This change allows users to configure these endpoints instead of being limited to the official Anthropic API.

Example Configuration

[providers.anthropic.minimax]
api_key = "your-api-key"
model = "MiniMax-M2.1"
base_url = "https://api.minimax.io/anthropic/v1/messages"

When base_url is not specified, it defaults to https://api.anthropic.com/v1/messages.

Compatibility

• No breaking changes - base_url is optional with a sensible default
• Existing configurations continue to work without modification

Note

There is an existing PR (#54) with similar functionality. This PR offers a more streamlined implementation:

• new() delegates to new_with_name() instead of duplicating code
• Minimal, focused changes without additional files (e.g., .gitignore updates)

If PR #54 is preferred, this PR can be closed.