refactor: migrate to ESM, update Bluesky agent, and clean repo sync
- Converted project to ES modules (`type: "module"` in package.json)
- Replaced BskyAgent with AtpAgent and updated login logic
- Removed `src/config.env`; now using `.env` for credentials
- Cleaned README formatting and minor typos
- Improved git remote handling:
* Adds Tangled remote if missing
* Ensures 'origin' push URL remains GitHub
* Adds clearer logging for pushes and warnings
- Updated utility functions:
* `run` now uses typed ExecSyncOptions
* `ensureTangledRecord` improved for error handling and deterministic TID generation
- General code cleanup: consistent formatting, optional chaining, and destructuring