feat(skill): add idiomatic-review skill

[KemingHe]

Related

• bug(general-doc-constraints): missing Unicode box drawing exception for tree output #99: GDC Unicode box drawing exception (may affect output formatting)
• feat(skill): add design-pattern-review skill #102: design-pattern-review skill (adjacent scope - structural patterns vs language idioms)

Problem

The current skill catalog covers documentation quality (documentation-review) and commit conventions (commit-message-creation) but has no skill for reviewing code against language-specific idiomatic patterns. Developers routinely write correct code that misses language-native constructs (e.g., Python's enumerate over range(len(...)), TypeScript's Record over manual index signatures). This gap is especially relevant during interview preparation and code review workflows where idiomatic fluency signals language depth.

Proposed Solution

Add an idiomatic-review skill to .agents/skills/ with the following capabilities:

• Auto language detection: Infer language from code syntax by default, with manual override parameter for ambiguous cases
• Triage tiers: Categorize suggestions by impact level
  • High: readability changes that affect how someone parses the code (e.g., unpacking, context managers, guard clauses)
  • Medium: standard library usage that eliminates hand-rolled logic (e.g., collections.Counter, itertools, zip)
  • Low: stylistic preference with no clear 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 idiomatic alternative | Doc link (when available) |

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

Sibling skills (design-pattern-review, #102) 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 official docs)
• No assets directory required for v1
• MIT licensed, language-agnostic

Alternatives Considered

• Extending senior-mentor to cover idiomatic review: rejected because senior-mentor is conversational and open-ended, while idiomatic review benefits from a structured checklist with triage output
• Per-language skills (e.g., python-review, typescript-review): rejected because the core review logic is language-agnostic and per-language skills fragment the catalog without proportional benefit