feat(cli): add show-plan flag to info command (#684)

* refactor: add io.Writer parameter to pretty print functions and JSON support

Generated-by: aiautocommit

* chore: promote tidwall/pretty from indirect to direct dependency

Generated-by: aiautocommit

* feat(cli): add show-plan flag to info command

- Add `--show-plan` flag to optionally render the generated build plan in the info command output.
- Update section header printing functions to accept an `io.Writer` destination for consistent output formatting.

Generated-by: aiautocommit