refactor(history): consolidate /diff and /version-summary into /history endpoint

Summary

• Removed GET /history/record/{id}/diff — absorbed into enhanced /history
• Removed GET /history/record/{id}/version-summary — absorbed into enhanced /history
• Enhanced GET /history/record/{id}/history with 3 new optional query params:
  • from_version + to_version — when both provided, includes diff between those versions in response
  • include_summary — when true, includes version summary counters in response
• Added RecordHistoryResponse schema with history, diff, and summary fields for a unified response structure
• Service methods and schemas kept unchanged — only the endpoint layer changed

Test plan

• GET /history/record/{id}/history → { "history": [...], "diff": null, "summary": null }
• GET /history/record/{id}/history?include_summary=true → summary populated with version counters
• GET /history/record/{id}/diff → 404 Not Found
• GET /history/record/{id}/version-summary → 404 Not Found

Checklist

• Code follows project API guidelines
• Documentation is updated (OpenAPI docs reflect removed endpoints and new params)
• Code adheres to project coding standards

Closes #122