Add Gemini 3.0 Flash model support

[vitali87]

📋 Task Description

Add support for Google's Gemini 3.0 Flash model to the codebase.

🎯 Acceptance Criteria

• Add Gemini 3.0 Flash model configuration
• Update model constants/enums
• Ensure compatibility with existing LLM integration
• Test model functionality

🔗 Related Files/Components

• File: codebase_rag/constants.py
• Component: LLM Integration

📝 Additional Context

Gemini 3.0 Flash is Google's latest fast inference model, offering improved performance and capabilities.

🚦 Priority

• High
• Medium
• Low

📊 Estimated Effort

• Small (< 2 hours)
• Medium (2-8 hours)
• Large (> 8 hours)