chore(api): mirror generation field in api types + PersonFormData (#689)

Manually mirrors the Spring Boot @Schema additions on PersonNodeDTO,
Person, and PersonUpdateDTO into the generated api.ts so the form +
gutter components compile against a finished type surface. The next
backend dev-profile run + `npm run generate:api` will regenerate the
same shape from the live OpenAPI spec.

PersonFormData gains `generation?: number | null` so PersonEditForm's
$state initialiser typechecks.

Refs #689

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

frontend/src/lib/person/person-validation.ts

@@ -11,6 +11,7 @@ export type PersonFormData = {
 	alias?: string | null;
 	birthYear?: number | null;
 	deathYear?: number | null;
+	generation?: number | null;
 	notes?: string | null;
 };