feat(skills): add design-patterns analyzer skill

Comprehensive GoF design patterns analyzer with stack-aware suggestions.

**Features**:
- Detects 23 GoF patterns (Creational, Structural, Behavioral)
- Stack detection (React, Angular, NestJS, Vue, Express, RxJS, Redux, ORMs)
- Code smell detection with pattern suggestions
- Quality evaluation (5 criteria scoring)
- Prefers stack-native alternatives (e.g., React Context over Singleton)

**Structure**:
- 9 files: SKILL.md + reference docs + detection rules + evaluation checklists
- 3 operating modes: Detection, Suggestion, Evaluation
- Pattern-specific documentation for all 23 GoF patterns

**Documentation**:
- Added comprehensive example in guide section 5.4
- Updated examples/README.md with skill entry
- Updated template count: 65 → 66

**Use cases**:
- Analyze existing patterns in codebase
- Suggest refactoring with stack-native patterns
- Evaluate pattern implementation quality

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

examples/README.md

@@ -56,6 +56,7 @@ Ready-to-use templates for Claude Code configuration.
 ### Skills
 | File | Purpose |
 |------|---------|
+| [design-patterns/](./skills/design-patterns/) | Detect and analyze GoF design patterns with stack-aware suggestions ⭐ |
 | [tdd-workflow.md](./skills/tdd-workflow.md) | Test-Driven Development process |
 | [security-checklist.md](./skills/security-checklist.md) | OWASP Top 10 security checks |
 | [pdf-generator.md](./skills/pdf-generator.md) | Professional PDF generation (Quarto/Typst) |