Refactor AI generation to integrate Gemini service and remove OpenAI dependencies

Commit notes

- Replaced OpenAIService with GeminiService in PackGenerator for AI sample pack generation. - Updated configuration to support Gemini API key alongside OpenAI API key. - Refactored prompt engineering to utilize Gemini's capabilities for generating pack names, sound lists, and metadata. - Removed OpenAI-related code and files to streamline the AI generation process.