feat(notification): add admin rest management and deletion

Add revision-safe service and template APIs, channel mapping, and validated admin controls.

Ref: IT-1601

HrynCo.NotificationService.DAL.EF/Repositories/NotificationServiceRepository.cs

@@ -20,6 +20,33 @@ internal sealed class NotificationServiceRepository(NotificationDbContext db, Te
         return service is null ? null : Map(service, await VersionCountsAsync(ct));
     }
 
+    public async Task<NotificationServiceInfo?> GetByNameAsync(string name, CancellationToken ct = default)
+    {
+        var service = await db.Services.AsNoTracking().Include(s => s.Languages).SingleOrDefaultAsync(s => s.Name == name, ct);
+        return service is null ? null : Map(service, await VersionCountsAsync(ct));
+    }
+
+    public async Task<bool> DeleteAsync(Guid id, Guid revision, CancellationToken ct = default)
+    {
+        var removed = false;
+        await mutations.ExecuteAsync(async () =>
+        {
+            if (revision == Guid.Empty)
+                throw new EmailTemplateWriteException("A nonempty service revision is required.", false);
+            var service = await db.Services.Include(s => s.Languages).SingleOrDefaultAsync(s => s.Id == id, ct);
+            if (service is null)
+                return;
+            if (service.Revision != revision)
+                throw new EmailTemplateWriteException("The service revision changed. Read it again before deleting.");
+            if (await db.TemplateDefinitions.AnyAsync(d => d.ServiceId == id, ct))
+                throw new EmailTemplateWriteException("Remove every template definition before deleting this service, including definitions without translations.");
+            db.ServiceLanguages.RemoveRange(service.Languages);
+            db.Services.Remove(service);
+            removed = true;
+        }, ct);
+        return removed;
+    }
+
     public Task SaveAsync(NotificationServiceInfo model, bool isNew, CancellationToken ct = default) => mutations.ExecuteAsync(async () =>
     {
         Validate(model);