feat(writing-skills): refactor skill to gold standard architecture

skills/writing-skills/references/tier-2-expanded/README.md

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+---
+description: When to use Tier 2 (Expanded) skill architecture.
+metadata:
+  tags: [tier-2, expanded, multi-file]
+---
+
+# Tier 2: Expanded Skills
+
+Multi-file skills for complex topics with multiple sub-concepts.
+
+## When to Use
+
+- **Multiple related concepts**: Needs separation of concerns
+- **200-1000 lines total**: Too big for one file
+- **Needs reference files**: Patterns, examples, troubleshooting
+- **Cross-linking**: Users need to navigate between sub-topics
+
+## Structure
+
+```
+my-skill/
+├── SKILL.md              # Overview + navigation
+└── references/
+    ├── core/
+    │   ├── README.md     # Main concept
+    │   └── api.md        # API reference
+    ├── patterns/
+    │   └── README.md     # Usage patterns
+    └── troubleshooting/
+        └── README.md     # Common issues
+```
+
+## Example
+
+The `writing-skills` skill itself is Tier 2:
+
+```
+writing-skills/
+├── SKILL.md              # Decision tree + navigation
+├── gotchas.md            # Tribal knowledge
+└── references/
+    ├── anti-rationalization/
+    ├── cso/
+    ├── standards/
+    ├── templates/
+    └── testing/
+```
+
+## Progressive Disclosure
+
+1. **Metadata** (~100 tokens): Name + description loaded at startup
+2. **SKILL.md** (<500 lines): Decision tree + index
+3. **References** (as needed): Loaded only when user navigates
+
+## Key Differences from Tier 1
+
+| Aspect | Tier 1 | Tier 2 |
+|--------|--------|--------|
+| Files | 1 | 5-20 |
+| Total lines | <200 | 200-1000 |
+| Decision logic | None | Simple tree |
+| Token cost | Minimal | Medium (progressive) |
+
+## Checklist
+
+- [ ] SKILL.md has clear navigation links
+- [ ] Each `references/` subdir has README.md
+- [ ] No circular references between files
+- [ ] Decision tree points to specific files