Refactor repo-utils into main, add Tangled record management and README sync
- Removed `repo-utils.ts` and moved its functions (`run`, `ensureDir`, `generateTid`, `ensureTangledRecord`, `updateReadme`) into `src/index.ts`.
- Improved Tangled record creation with caching and safe TID generation.
- Updated GitHub repo fetching and filtering logic.
- Added automatic README updates with Tangled mirror references.
- Upgraded TypeScript and ts-node versions in package.json.
- Expanded README.md with detailed setup, usage, and best practices instructions.
- Added VSCode spellcheck settings for project-specific words.