feat(skills): modernize capability-writing with Anthropic best practices

Updates capability-writing skill with progressive disclosure structure based on
Anthropic's January 2025 documentation. Implements Haiku-first approach (12x
cheaper, 2-5x faster than Sonnet).

Key changes:
- Add 5 core principles: conciseness, progressive disclosure, script bundling,
  degrees of freedom, and Haiku-first model selection
- Restructure with best-practices.md, templates/, examples/, and reference/
- Create 4 templates: user-invocable skill, background skill, agent, helper script
- Add 3 examples: simple workflow, progressive disclosure, with scripts
- Add 3 reference docs: frontmatter fields, model selection, anti-patterns
- Update create-capability to analyze complexity and recommend structures
- Default all new skills/agents to Haiku unless justified

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

skills/capability-writing/examples/progressive-disclosure.md

@@ -0,0 +1,129 @@
+# Example: Progressive Disclosure Skill
+
+A skill that uses reference files to keep the main SKILL.md concise.
+
+## Structure
+
+```
+skills/database-query/
+├── SKILL.md (~200 lines)
+├── reference/
+│   ├── schemas.md (table schemas)
+│   ├── common-queries.md (frequently used queries)
+│   └── optimization-tips.md (performance guidance)
+└── examples/
+    ├── simple-select.md
+    └── complex-join.md
+```
+
+## When to Use
+
+- Skill content would be >500 lines
+- Multiple domains or topics
+- Reference documentation is large
+- Want to keep main workflow concise
+
+## Example: database-query (main SKILL.md)
+
+```markdown
+---
+name: database-query
+description: >
+  Help users query the PostgreSQL database with proper schemas and optimization.
+  Use when user needs to write SQL queries or mentions database/tables.
+user-invocable: false
+---
+
+# Database Query Helper
+
+Help write efficient, correct SQL queries for our PostgreSQL database.
+
+## Quick Start
+
+\`\`\`sql
+SELECT id, name, created_at
+FROM users
+WHERE status = 'active'
+LIMIT 10;
+\`\`\`
+
+## Table Schemas
+
+We have 3 main schemas:
+
+- **Users & Auth**: See [reference/schemas.md#users](reference/schemas.md#users)
+- **Products**: See [reference/schemas.md#products](reference/schemas.md#products)
+- **Orders**: See [reference/schemas.md#orders](reference/schemas.md#orders)
+
+## Common Queries
+
+For frequently requested queries, see [reference/common-queries.md](reference/common-queries.md):
+- User activity reports
+- Sales summaries
+- Inventory status
+
+## Writing Queries
+
+1. **Identify tables**: Which schemas does this query need?
+2. **Check schema**: Load relevant schema from reference
+3. **Write query**: Use proper column names and types
+4. **Optimize**: See [reference/optimization-tips.md](reference/optimization-tips.md)
+
+## Examples
+
+- **Simple select**: See [examples/simple-select.md](examples/simple-select.md)
+- **Complex join**: See [examples/complex-join.md](examples/complex-join.md)
+```
+
+## Example: reference/schemas.md
+
+```markdown
+# Database Schemas
+
+## Users
+
+| Column | Type | Description |
+|--------|------|-------------|
+| id | UUID | Primary key |
+| email | VARCHAR(255) | Unique email |
+| name | VARCHAR(100) | Display name |
+| status | ENUM('active','inactive','banned') | Account status |
+| created_at | TIMESTAMP | Account creation |
+| updated_at | TIMESTAMP | Last update |
+
+## Products
+
+| Column | Type | Description |
+|--------|------|-------------|
+| id | UUID | Primary key |
+| name | VARCHAR(200) | Product name |
+| price | DECIMAL(10,2) | Price in USD |
+| inventory | INTEGER | Stock count |
+| category_id | UUID | FK to categories |
+
+## Orders
+
+[...more tables...]
+```
+
+## Why This Works
+
+- **Main file stays concise** (~200 lines)
+- **Details load on-demand**: schemas.md loads when user asks about specific table
+- **Fast for common cases**: Simple queries don't need reference files
+- **Scalable**: Can add more schemas without bloating main file
+
+## Loading Pattern
+
+1. User: "Show me all active users"
+2. Claude reads SKILL.md (sees Users schema reference)
+3. Claude: "I'll load the users schema to get column names"
+4. Claude reads reference/schemas.md#users
+5. Claude writes correct query
+
+## What Makes It Haiku-Friendly
+
+- ✓ Main workflow is simple ("identify → check schema → write query")
+- ✓ Reference files provide facts, not reasoning
+- ✓ Clear pointers to where details are
+- ✓ Examples show patterns