Fully implement Kavenegar SMS support

Core changes:
- ISmsService: add SendBulkAsync (batches of 200) + GetAccountInfoAsync
- KavenegarSmsService: POST requests, sender number config, bulk send
  via comma-separated receptors, account balance, full error code mapping
  (HTTP 400-432), enabled-flag check before any send
- SmsMarketingService: replaced per-recipient loop with SendBulkAsync
- SmsController: new GET /sms/balance endpoint returns Kavenegar credit
- SmsDtos: SmsBalanceDto
- IntegrationDtos + PlatformIntegrationService: SenderNumber field
- appsettings.json + docker-compose: Kavenegar__SenderNumber = 90005671

Dashboard:
- sms-screen: char counter, SMS parts indicator (Persian 70/67 chars,
  Latin 160/153), account balance card, sender line display, result banner

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

docker-compose.admin.yml

@@ -35,6 +35,7 @@ services:
       Cors__Origins__0: "${CORS_ADMIN_ORIGIN_0:-http://localhost:3102}"
       Cors__Origins__1: "${CORS_ORIGIN_0:-http://localhost:3101}"
       Kavenegar__ApiKey: "${KAVENEGAR_API_KEY:-}"
+      Kavenegar__SenderNumber: "${KAVENEGAR_SENDER:-90005671}"
     ports:
       - "${ADMIN_API_PORT:-5081}:8080"
     healthcheck: