Refactor plugin to use Gemini API

[snero]

This commit refactors the plugin to use the Gemini API instead of the Windsurf LLM API.

The language server dependency has been removed, and the authentication mechanism has been updated to use a Gemini API key. A new module for handling communication with the Gemini API has been implemented and integrated into the plugin's core logic.

The plugin has been renamed to "Gemini" to reflect the new backend, and all references to "Codeium" and "Windsurf" have been updated.

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[snero]

LGTM 🔥