Add SMS templates, prepaid IRT billing, and advertising shortcode 9000590009.

Charge ceil(len/64)*400 IRT per recipient across OTP, customer, and partner SMS; seed new businesses with 500k IRT; default partner sends to the advertising line.

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

src/customers/dto/send-customer-sms.dto.ts

@@ -1,8 +1,13 @@
-import { IsString, MaxLength, MinLength } from 'class-validator';
+import { IsOptional, IsString, MaxLength, MinLength } from 'class-validator';
 
 export class SendCustomerSmsDto {
   @IsString()
   @MinLength(1)
   @MaxLength(700)
   message!: string;
+
+  /** Optional SMS template id — body may still be sent as the rendered text. */
+  @IsOptional()
+  @IsString()
+  templateId?: string;
 }