feat(quality): add skill completeness checks

[jmagly]

Summary

This PR adds completeness checks to quality_checker.py, addressing G2.3 and G2.4 from the roadmap.

What's Included

New _check_skill_completeness() method that validates:

1. Prerequisites/Verification Sections

   • Patterns: prerequisites, requirements, before you start, verify that
   • Helps Claude check conditions before proceeding

2. Error Handling/Troubleshooting Guidance

   • Patterns: troubleshooting, common issues, if ... fails
   • Helps users recover from errors

3. Workflow Steps

   • Patterns: step 1, first, then, next, finally
   • Clear sequential guidance improves Claude's execution

Design Decisions

• Info-level messages only: These checks produce info messages, not warnings/errors
• This avoids penalizing existing skills while still providing helpful guidance
• Maintainers can later decide if any should become warnings

Roadmap Alignment

• G2.3: Add readability scoring → Workflow step detection addresses this
• G2.4: Add completeness checker ✅

Tests Included

4 new unit tests in TestCompletenessChecks:

• test_checker_detects_prerequisites_section
• test_checker_detects_troubleshooting_section
• test_checker_detects_workflow_steps
• test_checker_suggests_adding_prerequisites

Example Output (verbose mode)

ℹ️  INFO (completeness):
   ✓ Found verification/prerequisites section (SKILL.md)
   ✓ Found error handling/troubleshooting guidance (SKILL.md)
   ✓ Found clear workflow indicators (4 step markers) (SKILL.md)

Code Style

Follows existing patterns:

• Same _check_* method naming convention
• Same regex-based pattern matching approach
• Same report.add_info() call pattern
• 100 char lines, type hints, Google-style docstrings

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This PR builds on the Best Practices Guide (#206) - the patterns checked here match what that guide recommends.

Contributed by the AI Writing Guide project.