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.API/Models/Crm/SmsDtos.cs

@@ -10,3 +10,6 @@ public record SendSmsCampaignRequest(
 public record SmsCampaignResult(int SentCount, int FailedCount);
 
 public record SmsUsageDto(int UsedThisMonth, int MonthlyLimit, string Month);
+
+/// <summary>Kavenegar account credit balance returned to the dashboard.</summary>
+public record SmsBalanceDto(long RemainCredit, string AccountType, bool IsConfigured);