Add opt-in AST diagnostics for skill review without making Skills Guard stricter by default.
- Add hermes skills inspect --ast-deep to scan fetched skill bundles before installation
- Add hermes skills audit --deep to scan already-installed hub skills
- Keep AST analysis in tools/skills_ast_audit.py, separate from tools/skills_guard.py
- Label output as diagnostic hints, not security verdicts
- Cover dynamic import/access patterns: importlib, __import__(computed), getattr(computed), and __dict__[computed]
This follows the maintainer guidance from closed PR #7436: useful AST-level analysis belongs in an opt-in diagnostic path, not in Skills Guard's default heuristic scan.
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