feat(angular): Add metadata.json and README.md to all Angular skills

- Add metadata.json with version tracking, organization, and references
- Add README.md with skill overviews, usage guides, and quick references
- Brings Angular skills to parity with React Best Practices infrastructure
- Covers: angular, angular-state-management, angular-ui-patterns, angular-best-practices

skills/angular-ui-patterns/README.md

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+# Angular UI Patterns
+
+Modern UI patterns for building robust Angular applications optimized for AI agents and LLMs.
+
+## Overview
+
+This skill covers essential UI patterns for:
+
+- **Loading States** - Skeleton vs spinner decision trees
+- **Error Handling** - Error boundary hierarchy and recovery
+- **Progressive Disclosure** - Using `@defer` for lazy rendering
+- **Data Display** - Handling empty, loading, and error states
+- **Form Patterns** - Submission states and validation feedback
+- **Dialog/Modal Patterns** - Proper dialog lifecycle management
+
+## Core Principles
+
+1. **Never show stale UI** - Only show loading when no data exists
+2. **Surface all errors** - Never silently fail
+3. **Optimistic updates** - Update UI before server confirms
+4. **Progressive disclosure** - Use `@defer` to load non-critical content
+5. **Graceful degradation** - Fallback for failed features
+
+## Structure
+
+The `SKILL.md` file includes:
+
+1. **Golden Rules** - Non-negotiable patterns to follow
+2. **Decision Trees** - When to use skeleton vs spinner
+3. **Code Examples** - Correct vs incorrect implementations
+4. **Anti-patterns** - Common mistakes to avoid
+
+## Quick Reference
+
+```typescript
+// Only show loading without data
+if (error()) return <ErrorState />
+if (loading() && !data()) return <SkeletonState />
+if (!data()?.length) return <EmptyState />
+return <DataDisplay data={data()} />
+```
+
+## Version
+
+Current version: 1.0.0 (February 2026)
+
+## References
+
+- [Angular @defer](https://angular.dev/guide/defer)
+- [Angular Templates](https://angular.dev/guide/templates)