Extend skill validate with stylistic lint checks

[devrimcavusoglu]

Context

Current skill validate only checks structural correctness (required fields, valid values). It doesn't check for quality or style issues that could make a skill less effective.

Proposed Changes

• Add stylistic/quality checks beyond structural validation:
  • Body length heuristics (too short = likely incomplete)
  • "Too vague" detection (description lacking specifics)
  • Instruction quality scoring
  • Best practices enforcement (e.g., "Instructions should include step-by-step guidance")
• Stylistic issues should use a separate severity level (e.g., hint or style) to distinguish from structural errors/warnings

References

Analysis item 2.12