fix: Python 3.9 compatibility for HuggingFace Spaces

fix: add HuggingFace domains to ALLOWED_ORIGINS

fix: resolve all linting and formatting errors

refactor: reorganize project structure and add new features

fix: resolve SQL parameter binding and add enhanced upload feedback

feat: implement complete RAG application with frontend and backend

feat: implement core RAG services with TDD and enhanced pre-commit hooks

更新 .gitignore 以排除 .env.example 和新增上傳及儲存相關的檔案類型；擴充 requirements.txt，新增多個依賴項以支援 PDF 處理、資料庫連接及測試工具；修改 main.py，更新 FastAPI 應用程式的標題、版本及描述，並加入資料庫初始化的生命週期管理。

Add Next.js + FastAPI configuration for Hugging Face Spaces