Change only starter/rules_check.py. Standard library only.

• load_rule_files(directory) -> dict[str, str]: read the text of every present rule file among AGENTS.md, CLAUDE.md, .cursorrules.
• is_pointer(text) -> bool: true when the file is a thin pointer — at most 10 non-empty lines and at least one line referencing AGENTS.md.
• check_directory(directory) -> dict returning {"source": "AGENTS.md", "ok": bool, "files": [...]}:
  • AGENTS.md missing or empty produces a missing-source entry and ok=False.
  • A present, non-empty AGENTS.md produces a source entry.
  • Every other rule file is classified: pointer (thin pointer), copy (exact match of AGENTS.md content), or diverged (anything else), each with an issues list; diverged entries carry a reason naming the difference from AGENTS.md.
  • ok=True only when every entry is source, pointer, or copy.
• main(argv=None) -> int:
  • Exactly one argument (the directory). Otherwise print usage to stderr and return 2.
  • Print ok=... files=... diverged=... to stdout; return 0 when ok, otherwise 1.

Done means python verify.py starter exits 0 with all eleven tests passing.