docs(jin-frame): add version table, improve inheritance/retry examples in README

[imjuni]

Summary

• Version 표 추가 — v5.0 미만은 Axios, v5.0 이상은 native fetch 명시
• Inheritance 섹션 개선 — getDefaultValues로 공통 필드 기본값 자동 주입하는 실전 패턴 예시 (PokeAPI 기반)
• Retry/Timeout 섹션 확장 — 지수 백오프(getInterval) 예시 및 _execute() 레벨 override 예시 추가

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (03550d9) to head (4c26d1f).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

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  Coverage   100.00%   100.00%           
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  Files          107       107           
  Lines         1089      1089           
  Branches       293       293           
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  Hits          1089      1089           

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