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.Core/Interfaces/ISmsService.cs

@@ -1,7 +1,23 @@
 namespace Meezi.Core.Interfaces;
 
+public record KavenegarAccountInfo(long RemainCredit, string AccountType);
+
+public record BulkSendResult(int SentCount, int FailedCount);
+
 public interface ISmsService
 {
+    /// <summary>Send a one-time password via Kavenegar Verify/Lookup template.</summary>
     Task SendOtpAsync(string phone, string otp, CancellationToken cancellationToken = default);
+
+    /// <summary>Send a plain-text message to a single recipient.</summary>
     Task SendMessageAsync(string phone, string message, CancellationToken cancellationToken = default);
+
+    /// <summary>
+    /// Send the same message to many recipients in batches of up to 200.
+    /// Never throws — failures per batch are counted and returned.
+    /// </summary>
+    Task<BulkSendResult> SendBulkAsync(IReadOnlyList<string> phones, string message, CancellationToken cancellationToken = default);
+
+    /// <summary>Returns credit balance from the Kavenegar account, or null if not configured.</summary>
+    Task<KavenegarAccountInfo?> GetAccountInfoAsync(CancellationToken cancellationToken = default);
 }