Add customer Excel import/export and Gama bulk SMS sending.

Business SMS uses optional settings.sms.senderNumber (else advertising shortcode) with SendQuick for one recipient and SendBulk for quantity.

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

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

@@ -59,4 +59,16 @@ export class UpdateBusinessDto {
   @ValidateIf((_, value) => value !== null)
   @IsDateString()
   annualRenewalAt?: string | null;
+
+  /**
+   * Business SMS shortcode for customer messages (e.g. 5000123456).
+   * Empty string or null clears it (falls back to Meshkee advertising number).
+   */
+  @IsOptional()
+  @ValidateIf((_, value) => value !== null && value !== '')
+  @IsString()
+  @Matches(/^\d{8,16}$/, {
+    message: 'smsSenderNumber must be an 8–16 digit shortcode',
+  })
+  smsSenderNumber?: string | null;
 }