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.yml

@@ -81,6 +81,7 @@ services:
       Cors__Origins__2: "${CORS_ORIGIN_2:-http://localhost:3103}"
       Auth__MaxOtpAttemptsPerHour: "${OTP_RATE_LIMIT:-100}"
       Kavenegar__ApiKey: "${KAVENEGAR_API_KEY:-}"
+      Kavenegar__SenderNumber: "${KAVENEGAR_SENDER:-90005671}"
       Snappfood__WebhookSecret: "${SNAPPFOOD_WEBHOOK_SECRET:-meezi-dev-snappfood-secret}"
       ZarinPal__MerchantId: "${ZARINPAL_MERCHANT_ID:-}"
       ZarinPal__Sandbox: "${ZARINPAL_SANDBOX:-true}"