Adds the optional generation field to both DTOs:
- PersonUpsertCommand gains Integer generation in the canonical-import
builder chain; service wiring lands in the next commit.
- PersonUpdateDTO gains @Min(0)@Max(10) Integer generation, the form-path
surface. The constraints mirror the V70 CHECK so validation fails fast
at the controller before reaching the DB.
PersonControllerTest pins the validation behaviour: -1 → 400, 11 → 400,
null → 200, 3 → 200 for both PUT (update) and POST (create) paths. The
GlobalExceptionHandler maps MethodArgumentNotValidException to
VALIDATION_ERROR so the frontend's extractErrorCode keeps working.
Refs #689
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
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