feat: migrate to WSL Ubuntu native development environment

從 Docker/macOS+Conda 部署遷移到 WSL2 Ubuntu 原生開發環境

主要變更：
- 移除所有 Docker 相關配置檔案 (Dockerfile, docker-compose.yml, .dockerignore 等)
- 移除 macOS/Conda 設置腳本 (SETUP.md, setup_conda.sh)
- 新增 WSL Ubuntu 自動化環境設置腳本 (setup_dev_env.sh)
- 新增後端/前端快速啟動腳本 (start_backend.sh, start_frontend.sh)
- 統一開發端口配置 (backend: 8000, frontend: 5173)
- 改進資料庫連接穩定性（連接池、超時設置、重試機制）
- 更新專案文檔以反映當前 WSL 開發環境

Technical improvements:
- Database connection pooling with health checks and auto-reconnection
- Retry logic for long-running OCR tasks to prevent DB timeouts
- Extended JWT token expiration to 24 hours
- Support for Office documents (pptx, docx) via LibreOffice headless
- Comprehensive system dependency installation in single script

Environment:
- OS: WSL2 Ubuntu 24.04
- Python: 3.12 (venv)
- Node.js: 24.x LTS (nvm)
- Backend Port: 8000
- Frontend Port: 5173

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

backend/app/services/office_converter.py

@@ -42,14 +42,16 @@ class OfficeConverter:
     def _verify_libreoffice(self):
         """Verify LibreOffice is installed and accessible"""
         if not Path(self.libreoffice_path).exists():
-            # Try alternative path for Homebrew installation
+            # Try alternative path (system-wide installation)
             alt_path = shutil.which("soffice")
             if alt_path:
                 self.libreoffice_path = alt_path
                 logger.info(f"Using LibreOffice at: {alt_path}")
             else:
                 raise OfficeConverterError(
-                    "LibreOffice not found. Please install LibreOffice: brew install libreoffice"
+                    "LibreOffice not found. Please install LibreOffice:\n"
+                    "  Ubuntu/Debian: sudo apt install -y libreoffice-writer libreoffice-impress libreoffice-core-nogui\n"
+                    "  macOS: brew install libreoffice"
                 )
 
     def is_office_document(self, file_path: Path) -> bool: