refactor: rename domain types and introduce TransactionBehavior pattern

- Rename Template -> EmailTemplate, Provider -> EmailChannel,
  ProviderSettings -> EmailChannelSettings, ProviderType -> EmailChannelType,
  ProviderUsage -> EmailChannelUsage throughout all layers
- Add Undefined = 0 to EmailChannelType enum for safe default handling
- Remove SaveChangesAsync from EfRepository methods — repositories now only stage changes
- Add SaveChangesAsync to IUnitOfWork and EfUnitOfWork
- Add TransactionBehavior MediatR pipeline: wraps every handler in a transaction,
  saves and commits on success, rolls back on exception
- Add MediatR package reference to Services project

Ref: IT-628

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

HrynCo.NotificationService.DAL.Abstract/IUnitOfWork.cs

@@ -2,6 +2,7 @@ namespace HrynCo.NotificationService.DAL.Abstract;
 
 public interface IUnitOfWork
 {
+    Task SaveChangesAsync(CancellationToken cancellationToken = default);
     Task<ITransaction> BeginTransactionAsync(CancellationToken cancellationToken = default);
     ITransaction? GetCurrentTransaction();
 

HrynCo.NotificationService.DAL.Abstract/Providers/EmailChannel.cs

@@ -2,14 +2,14 @@ using HrynCo.NotificationService.DAL.Abstract.Entities;
 
 namespace HrynCo.NotificationService.DAL.Abstract.Providers;
 
-public class Provider : Entity
+public class EmailChannel : Entity
 {
     public required string ServiceName { get; set; }
     public int Priority { get; set; }
-    public ProviderType ProviderType { get; set; }
-    public required ProviderSettings Settings { get; set; }
+    public EmailChannelType EmailChannelType { get; set; }
+    public required EmailChannelSettings Settings { get; set; }
     public int? DailyLimit { get; set; }
     public int? MonthlyLimit { get; set; }
     public int WarnThresholdPercent { get; set; } = 90;
     public bool IsActive { get; set; } = true;
-}
+}

HrynCo.NotificationService.DAL.Abstract/Providers/EmailChannelSettings.cs

@@ -1,13 +1,13 @@
 namespace HrynCo.NotificationService.DAL.Abstract.Providers;
 
-public abstract class ProviderSettings
+public abstract class EmailChannelSettings
 {
-    public abstract ProviderType ProviderType { get; }
+    public abstract EmailChannelType EmailChannelType { get; }
 }
 
-public class SmtpProviderSettings : ProviderSettings
+public class SmtpChannelSettings : EmailChannelSettings
 {
-    public override ProviderType ProviderType => ProviderType.Smtp;
+    public override EmailChannelType EmailChannelType => EmailChannelType.Smtp;
 
     public required string Host { get; set; }
     public int Port { get; set; } = 587;

HrynCo.NotificationService.DAL.Abstract/Providers/EmailChannelType.cs

@@ -1,6 +1,7 @@
 namespace HrynCo.NotificationService.DAL.Abstract.Providers;
 
-public enum ProviderType
+public enum EmailChannelType
 {
+    Undefined = 0,
     Smtp = 1
 }

HrynCo.NotificationService.DAL.Abstract/Providers/EmailChannelUsage.cs

@@ -3,10 +3,10 @@ using HrynCo.NotificationService.DAL.Abstract.Entities;
 namespace HrynCo.NotificationService.DAL.Abstract.Providers;
 
 /// <summary>
-/// Tracks email send counts per provider per calendar day.
+/// Tracks email send counts per EmailChannel per calendar day.
 /// Monthly counts are derived by summing daily records within a month.
 /// </summary>
-public class ProviderUsage : Entity
+public class EmailChannelUsage : Entity
 {
     public Guid ProviderId { get; set; }
     public DateOnly Date { get; set; }

HrynCo.NotificationService.DAL.Abstract/Repositories/IEmailChannelRepository.cs

@@ -0,0 +1,12 @@
+using HrynCo.NotificationService.DAL.Abstract.Providers;
+
+namespace HrynCo.NotificationService.DAL.Abstract.Repositories;
+
+public interface IEmailChannelRepository
+{
+    Task<IReadOnlyList<EmailChannel>> GetByServiceAsync(string serviceName, CancellationToken ct = default);
+    Task<EmailChannel?> GetByIdAsync(Guid id, CancellationToken ct = default);
+    Task AddAsync(EmailChannel channel, CancellationToken ct = default);
+    Task UpdateAsync(EmailChannel channel, CancellationToken ct = default);
+    Task DeleteAsync(EmailChannel channel, CancellationToken ct = default);
+}

HrynCo.NotificationService.DAL.Abstract/Repositories/IEmailChannelUsageRepository.cs

@@ -2,9 +2,9 @@ using HrynCo.NotificationService.DAL.Abstract.Providers;
 
 namespace HrynCo.NotificationService.DAL.Abstract.Repositories;
 
-public interface IProviderUsageRepository
+public interface IEmailChannelUsageRepository
 {
     Task<int> GetDailyCountAsync(Guid providerId, DateOnly date, CancellationToken ct = default);
     Task<int> GetMonthlyCountAsync(Guid providerId, int year, int month, CancellationToken ct = default);
-    Task IncrementAsync(Guid providerId, DateOnly date, CancellationToken ct = default);
+    Task IncrementUsageAsync(Guid providerId, DateOnly date, CancellationToken ct = default);
 }

HrynCo.NotificationService.DAL.Abstract/Repositories/IEmailTemplateRepository.cs

@@ -0,0 +1,12 @@
+using HrynCo.NotificationService.DAL.Abstract.Templates;
+
+namespace HrynCo.NotificationService.DAL.Abstract.Repositories;
+
+public interface IEmailEmailTemplateRepository
+{
+    Task<IReadOnlyList<EmailTemplate>> GetByServiceAsync(string serviceName, CancellationToken ct = default);
+    Task<EmailTemplate?> GetAsync(string serviceName, string key, string languageCode, CancellationToken ct = default);
+    Task AddAsync(EmailTemplate EmailTemplate, CancellationToken ct = default);
+    Task UpdateAsync(EmailTemplate EmailTemplate, CancellationToken ct = default);
+    Task DeleteAsync(EmailTemplate EmailTemplate, CancellationToken ct = default);
+}

HrynCo.NotificationService.DAL.Abstract/Repositories/IProviderRepository.cs

@@ -1,12 +0,0 @@
-using HrynCo.NotificationService.DAL.Abstract.Providers;
-
-namespace HrynCo.NotificationService.DAL.Abstract.Repositories;
-
-public interface IProviderRepository
-{
-    Task<IReadOnlyList<Provider>> GetByServiceAsync(string serviceName, CancellationToken ct = default);
-    Task<Provider?> GetByIdAsync(Guid id, CancellationToken ct = default);
-    Task AddAsync(Provider provider, CancellationToken ct = default);
-    Task UpdateAsync(Provider provider, CancellationToken ct = default);
-    Task DeleteAsync(Provider provider, CancellationToken ct = default);
-}

HrynCo.NotificationService.DAL.Abstract/Repositories/ITemplateRepository.cs

@@ -1,12 +0,0 @@
-using HrynCo.NotificationService.DAL.Abstract.Templates;
-
-namespace HrynCo.NotificationService.DAL.Abstract.Repositories;
-
-public interface ITemplateRepository
-{
-    Task<IReadOnlyList<Template>> GetByServiceAsync(string serviceName, CancellationToken ct = default);
-    Task<Template?> GetAsync(string serviceName, string key, string languageCode, CancellationToken ct = default);
-    Task AddAsync(Template template, CancellationToken ct = default);
-    Task UpdateAsync(Template template, CancellationToken ct = default);
-    Task DeleteAsync(Template template, CancellationToken ct = default);
-}

HrynCo.NotificationService.DAL.Abstract/Templates/EmailTemplate.cs

@@ -2,7 +2,7 @@ using HrynCo.NotificationService.DAL.Abstract.Entities;
 
 namespace HrynCo.NotificationService.DAL.Abstract.Templates;
 
-public class Template : Entity
+public class EmailTemplate : Entity
 {
     public required string ServiceName { get; set; }
     public required string Key { get; set; }
@@ -10,5 +10,5 @@ public class Template : Entity
     public required string Subject { get; set; }
     public required string HtmlBody { get; set; }
     public required string TextBody { get; set; }
-    public IReadOnlyList<TemplateVariable> Variables { get; set; } = [];
+    public IReadOnlyList<EmailTemplateVariable> Variables { get; set; } = [];
 }

HrynCo.NotificationService.DAL.Abstract/Templates/TemplateVariable.cs

@@ -1,6 +1,6 @@
 namespace HrynCo.NotificationService.DAL.Abstract.Templates;
 
-public record TemplateVariable
+public record EmailTemplateVariable
 {
     public required string Name { get; init; }
     public bool Required { get; init; }