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>

src/Meezi.Admin.API/Models/IntegrationDtos.cs

@@ -26,6 +26,7 @@ public record KavenegarConfigDto(
     bool IsEnabled,
     string? ApiKey,
     string OtpTemplate,
+    string SenderNumber,
     bool HasStoredApiKey);
 
 public record OpenAiIntegrationConfigDto(
@@ -92,7 +93,8 @@ public record UpdatePaymentGatewayRequest(
 public record UpdateKavenegarRequest(
     bool IsEnabled,
     string? ApiKey,
-    string OtpTemplate);
+    string OtpTemplate,
+    string SenderNumber);
 
 public record AdminNotificationRowDto(
     string Id,