[Code scan] Do not recommend unsupported dpgen --version in simplify skill

[njzjz]

This issue is from a Codex global scan of the repository.

The bundled dpgen-simplify skill tells users/agents to verify DP-GEN with dpgen --version, but the DP-GEN CLI does not define a --version option.

Evidence:

dpgen/skills/dpgen-simplify/SKILL.md

Lines 100 to 107 in 7af5246

	### 4.1 Outer launcher policy
	Use an activated DP-GEN environment and verify with:
	```bash
	dpgen --version
	```

dpgen/skills/dpgen-simplify/SKILL.md

Lines 274 to 282 in 7af5246

	## Validation before run
	Before execution, validate the workflow in this order:
	1. confirm outer-layer `dpgen` is available:
	```bash
	dpgen --version
	```

dpgen/dpgen/main.py

Lines 39 to 47 in 7af5246

	parser = argparse.ArgumentParser(
	description="""
	dpgen is a convenient script that uses DeepGenerator to prepare initial
	data, drive DeepMDkit and analyze results. This script works based on
	several sub-commands with their own options. To see the options for the
	sub-commands, type "dpgen sub-command -h"."""
	)
	subparsers = parser.add_subparsers()

main_parser() only configures the default argparse help and subcommands; main_parser().parse_args(["--version"]) exits with status 2. Existing user-facing guidance commonly uses dpgen -h for installation checks.

Expected behavior: update the skill instructions to use a supported validation command such as dpgen -h, or add a real --version option to the CLI.