feat(skill): add design-pattern-review skill

[KemingHe]

Related

• feat(skill): add idiomatic-review skill #101: idiomatic-review skill (adjacent scope - language idioms vs structural patterns)

Problem

The skill catalog will cover language-level idioms (idiomatic-review, #101) but has no skill for reviewing code against structural design patterns at the function, class, and component level. Developers routinely produce working code that hard-codes dependencies, nests conditionals deeply, or uses inheritance where composition is simpler. These patterns affect testability, readability, and changeability - concerns distinct from language idiom usage.

Proposed Solution

Add a design-pattern-review skill to .agents/skills/ with the following capabilities:

• Auto language detection: Infer language from code syntax by default, with manual override for ambiguous cases
• Triage tiers: Categorize suggestions by impact level
  • High: structural changes that affect testability or changeability (e.g., hard-coded dependencies to DI, deep nesting to guard clauses)
  • Medium: pattern application that reduces complexity (e.g., strategy pattern over switch blocks, composition over inheritance)
  • Low: stylistic structural preference with no clear testability or readability win (surfaced only on request)
• Triage report template: Structured output format for consistent, scannable results

| Tier | Location | Current Pattern | Suggested Pattern | Reference |
| :--- | :--- | :--- | :--- | :--- |
| High/Medium/Low | File + line range or function/class name | What the code does now | The structural alternative | Doc link (when available) |

• Official docs lookup: Link suggestions to canonical pattern references when web search or MCP tools are available
• Graceful degradation: Fully functional without network access - omits reference links, retains all review capability
• Composability: Standalone invocation or seamless use within other skills (e.g., senior-mentor sessions) via loose coupling

Sibling skills (idiomatic-review, #101) use a parallel triage report format. This skill defines its own template independently for self-containment, but implementers should align with the shared format where possible.

Design targets:

• ~50 lines SKILL.md body (under 500-line and 5000-token limits per skill-creation spec)
• SBP block included (web search for pattern references)
• No assets directory required for v1
• MIT licensed, language-agnostic

Alternatives Considered

• Combining with idiomatic-review (feat(skill): add idiomatic-review skill #101): rejected because language idioms (expression-level) and design patterns (structural-level) are distinct review concerns with different triage criteria and reference sources
• Extending senior-mentor: rejected because senior-mentor is a thinking mode for design reasoning, not a structured review tool with triage output