many fixes and improvements - rework for modules/ and common/

feat(emailer): add Postmark and Resend providers

backend/Modules/Memberships/Handlers/CancelMembership.cs

@@ -0,0 +1,49 @@
+using Hutopy.Modules.Memberships.Contracts;
+using Hutopy.Modules.Memberships.Data;
+
+namespace Hutopy.Modules.Memberships.Handlers;
+
+[PublicAPI]
+public class CancelMembershipRequest
+{
+    public Guid SubscriptionId { get; set; }
+}
+
+public class CancelMembershipHandler(
+    MembershipsDbContext dbContext,
+    IMembershipCancellationProcessor cancellationProcessor)
+    : Endpoint<CancelMembershipRequest>
+{
+    public override void Configure()
+    {
+        Delete("/api/memberships");
+        Options(o => o.WithTags("Memberships"));
+    }
+    
+    public override async Task HandleAsync(
+        CancelMembershipRequest req,
+        CancellationToken ct)
+    {
+        var subscription = await dbContext
+            .Memberships
+            .FindAsync(
+                [req.SubscriptionId],
+                cancellationToken: ct);
+
+        if (subscription is not { EndDate: null } 
+            || subscription.StripeSubscriptionId is null)
+        {
+            await SendNotFoundAsync(ct);
+            return;
+        }
+
+        // Cancel Stripe subscription
+        await cancellationProcessor.CancelAsync(subscription.StripeSubscriptionId, ct);
+
+        // Update subscription in the system
+        subscription.EndDate = DateTime.UtcNow;
+        await dbContext.SaveChangesAsync(ct);
+
+        await SendOkAsync(subscription.Id, ct);
+    }
+}