Problem

Sensei v1.3.0 has advisory check 17 — body structure quality — checking whether the SKILL.md body follows effective instruction patterns:

1. Actionable instructions (code blocks, steps, commands)
2. Examples section (input → expected output scenarios)
3. Error handling (failure modes, recovery steps)
4. Troubleshooting (common problems, fixes)

Waza has no body quality checks.

Expected Behavior

Add a BodyStructureChecker to internal/checks/ that:

• Scans SKILL.md body (below frontmatter) for structure signals
• Detects: code blocks, numbered steps, "Example:", "Error:", "Troubleshooting:" sections
• Advisory only — surfaces recommendations, does not block

References

• spboyer/sensei references/scoring.md — advisory check 17
• Anthropic Complete Guide to Building Skills — recommended body structure

Acceptance Criteria

• New checker in internal/checks/
• Detects actionable instructions vs declarative-only
• Detects examples section
• Detects error handling / troubleshooting
• Advisory status
• Tests