chore: migrate to uv pyproject.toml for dependency management

- Add pyproject.toml with project dependencies
- Remove inline script metadata from yaml2pptx.py
- Update openspec/config.yaml development guidelines
- Update README.md and README_DEV.md documentation
- Archive change: migrate-to-uv-package-management

yaml2pptx.py

@@ -1,14 +1,4 @@
 #!/usr/bin/env python3
-# /// script
-# requires-python = ">=3.8"
-# dependencies = [
-#     "python-pptx",
-#     "pyyaml",
-#     "flask",
-#     "watchdog",
-# ]
-# ///
-
 """
 YAML to PPTX Converter
 将 YAML 格式的演示文稿源文件转换为 PPTX 文件