Adds the `-a` short flag, improves CLI validation for one-shot mode,
and ensures `--model` takes precedence over `--pick-model`.
BREAKING CHANGE: `--task-attachment` has been renamed to `--attach`.
Moves script logic to `browser/script/` for shared use. Implements
message rollback on API failure, caches environment variables, and
fixes a potential panic in the spinner.
- Relocate Command, Recorder, and Verifier to `src/browser/script/`
- Implement message rollback on API and synthesis failures in Agent
- Cache `LP_*` environment variables process-wide with mutex protection
- Fix potential panic in Spinner during backward clock jumps
- Improve Recorder to handle write failures and multi-line comments
- Update documentation regarding attachments and path safety
