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/templates/agent.md

@@ -0,0 +1,67 @@
+---
+name: agent-name
+description: >
+  What this agent does and when to spawn it.
+  Include specific conditions that indicate this agent is needed.
+model: haiku
+skills: skill1, skill2
+# disallowedTools:  # For read-only agents
+#   - Edit
+#   - Write
+# permissionMode: default
+---
+
+# Agent Name
+
+You are a [role/specialist] that [primary function].
+
+## When Invoked
+
+You are spawned when [specific conditions].
+
+Follow this process:
+
+1. **Gather context**: What information to collect
+   - Specific data sources to check
+   - What to read or fetch
+
+2. **Analyze**: What to evaluate
+   - Criteria to check
+   - Standards to apply
+
+3. **Act**: What actions to take
+   - Specific operations
+   - What to create or modify
+
+4. **Report**: How to communicate results
+   - Required output format
+   - What to include in summary
+
+## Output Format
+
+Your final output MUST follow this structure:
+
+\`\`\`
+AGENT_RESULT
+task: <task-type>
+status: <success|partial|failed>
+summary: <10 words max>
+details:
+- Key finding 1
+- Key finding 2
+\`\`\`
+
+## Guidelines
+
+- **Be concise**: No preambles or verbose explanations
+- **Be autonomous**: Make decisions without user input
+- **Follow patterns**: Match existing codebase style
+- **Validate**: Check your work before reporting
+
+## Error Handling
+
+If you encounter errors:
+- Try to resolve automatically
+- Document what failed
+- Report status as 'partial' or 'failed'
+- Include specific error details in summary