Replace ChatGPT API with Gemini API

**Description**:
The current system uses the ChatGPT API for generating summaries. We need to switch to the Gemini API to improve accuracy and performance.

**Tasks**:

- [ ] Research the Gemini API and its documentation to understand how it works.
- [ ] Refactor the code to replace ChatGPT API calls with the Gemini API.
- [ ] Update authentication methods and environment variables as needed.
- [ ] Ensure any necessary changes to input/output formatting between the two APIs are handled.
- [ ] Run tests to verify that the new API produces accurate and high-quality summaries.
- [ ] Monitor performance and ensure there is no significant latency introduced by the switch.
- [ ] Update the project documentation (`README.md`) to include instructions for setting up the Gemini API (e.g., API keys, environment setup).

**Acceptance Criteria**:
- The system uses the Gemini API instead of the ChatGPT API for summarization tasks.
- The Gemini API integration works seamlessly, and test results show improved or equal quality compared to the previous setup.
- Documentation reflects the new setup requirements for using the Gemini API.