Add diff command for Patchlogr CLI

[toothlessdev]

🧩 Summary

• @patchlogr/cli 패키지를 위한 diff command 를 추가합니다

🎯 Context

🛠 Proposed Change

• preprocessOASDocument 로 전처리
• method, tag 별로 파티셔닝
• diffSpec 으로 changeset, versionbump 산출

📦 Scope

• @patchlogr/core
• @patchlogr/cli
• @patchlogr/inspector
• docs, examples
• tests
• ci / infra
• other (아래에 명시)

⚠️ Impact & Risk

• No Breaking Changes
• Possible Breaking Changes