Ship legacy migrate APIs, portfolio/blog old-id schema, and admin migrate/purge flows.

Co-authored-by: Cursor <cursoragent@cursor.com>

src/business-admin/dto/update-business.dto.ts

@@ -3,6 +3,7 @@ import {
   IsArray,
   IsInt,
   IsOptional,
+  IsPositive,
   IsString,
   Matches,
   MinLength,
@@ -44,4 +45,12 @@ export class UpdateBusinessDto {
   @Type(() => Number)
   @IsInt()
   ownerUserId?: number | null;
+
+  /** Legacy WillaEngine businesses.id; null clears the link. */
+  @IsOptional()
+  @ValidateIf((_, value) => value !== null)
+  @Type(() => Number)
+  @IsInt()
+  @IsPositive()
+  oldBusinessId?: number | null;
 }