Add skill quality validator for skill metadata and workflow checks

[SayanDey322]

Summary

Implemented a lightweight skill quality validator to improve consistency across SKILL.md files.

Changes

• Added tools/skill_quality_validator.py
• Validates required frontmatter fields
• Detects weak tags
• Checks required sections
• Reports warnings and failures
• Supports validation of all skills under the skills directory

Testing

python tools/skill_quality_validator.py skills/

Issue: #86

[mukul975]

Thanks for this. A few blocking issues, and a direction note:

1. Committed scratch output. This PR commits tools/skill_quality_validator_output.txt, _output2.txt, and _output3.txt — generated tool logs that shouldn't land in the repo. Please remove all three.
2. Parallel validator overlap. This adds a standalone tools/skill_quality_validator.py alongside the existing tools/validate-skill.py. The repo should have one validator, not two. PR #87 (nested-name fix) is already merged into validate-skill.py, and #88 is extending that same file with tag-quality/workflow/prereq checks — which overlaps much of what this PR does.
3. Direction. Rather than a second validator, please fold any genuinely new checks here into the existing validate-skill.py (coordinate with #88 to avoid duplication). If everything here is already covered by #87 + #88, this PR can be closed as subsumed.

(Note: #92, the exact duplicate of this PR, has been closed; this is the surviving one.)