Add Gemini Provider Support with Custom Base URL Configuration

[ericproulx]

Summary

This PR adds support for configuring custom base URLs for the Gemini provider in SwarmSDK, enabling agents to use Google's Gemini API through custom endpoints or proxies.

Changes

• LLM Configuration: Extended lib/swarm_sdk/agent/chat_helpers/llm_configuration.rb to handle Gemini provider when a custom base_url is specified

  • Configures gemini_api_base from the provided base URL
  • Retrieves and sets gemini_api_key from SwarmSDK configuration

• Test Coverage: Added test_initialization_with_base_url_and_gemini_provider in test/swarm_sdk/agent/chat_test.rb

  • Verifies that Agent::Chat can be initialized with Gemini provider and custom base URL
  • Ensures proper handling of Gemini API key from environment variables

Technical Details

The implementation follows the same pattern as other providers (OpenAI, Anthropic, Ollama, GPUStack) by:

1. Checking if the provider is "gemini" in the base_url configuration block
2. Setting the gemini_api_base configuration option
3. Retrieving and setting the API key from SwarmSDK configuration

Test Plan

• Added unit test for Gemini provider with custom base_url
• Test verifies successful Agent::Chat initialization
• Test properly manages API key environment variable
• Manual testing with actual Gemini API endpoint (recommended before merge)

Impact

• Low risk: Adds new functionality without modifying existing provider behavior
• Enables users to configure Gemini models with custom endpoints
• Maintains consistency with existing provider configuration patterns