Organize backend into product executable and shared Go modules

backend/shared/database/transaction/transaction.go

@@ -0,0 +1,11 @@
+package transaction
+
+import (
+	"context"
+)
+
+type Callback = func(ctx context.Context) (any, error)
+
+type Transaction interface {
+	Execute(ctx context.Context, cb Callback) (any, error)
+}