- Use DeepSeek API (api.deepseek.com) with openai-go SDK
- Replace OPENAI_MODEL env var with DEEPSEEK_MODEL
- Default model: deepseek-v4-pro
- API key read from DEEPSEEK_API_KEY env var
This commit standardizes the naming of identifier and API key fields
across the codebase to use consistent camel case (e.g., `ID`, `APIKey`,
`DatabaseURL`). This includes updates to struct fields, method names,
function parameters, and environment variable references. The changes
improve code clarity and maintainability by reducing ambiguity and
aligning with Go naming conventions. No functional behavior is changed.
