feat(person): generation on PersonUpsertCommand + PersonUpdateDTO (#689)

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>

backend/src/main/java/org/raddatz/familienarchiv/person/PersonUpdateDTO.java

@@ -1,5 +1,7 @@
 package org.raddatz.familienarchiv.person;
 
+import jakarta.validation.constraints.Max;
+import jakarta.validation.constraints.Min;
 import jakarta.validation.constraints.NotNull;
 import jakarta.validation.constraints.Size;
 import lombok.Data;
@@ -21,4 +23,9 @@ public class PersonUpdateDTO {
     private String notes;
     private Integer birthYear;
     private Integer deathYear;
+    // Mirror of the persons.generation CHECK constraint (V70).
+    // null clears the field; 0..10 is the allowlist of valid indices.
+    @Min(0)
+    @Max(10)
+    private Integer generation;
 }

backend/src/main/java/org/raddatz/familienarchiv/person/PersonUpsertCommand.java

@@ -18,6 +18,7 @@ public record PersonUpsertCommand(
         String notes,
         Integer birthYear,
         Integer deathYear,
+        Integer generation,
         boolean familyMember,
         PersonType personType,
         boolean provisional