feat(shipments): add ShipmentProviderInterface and ShipmentProviderRegistry

- Introduced ShipmentProviderInterface to define the contract for shipment providers.
- Implemented ShipmentProviderRegistry to manage and retrieve shipment providers.
- Added a new tool for probing Apaczka order_send payload variants, enhancing debugging capabilities.

resources/scss/app.scss

@@ -303,6 +303,21 @@ details[open] > .sidebar__group-toggle .sidebar__toggle-arrow {
   font-weight: 700;
 }
 
+h2.section-title,
+h3.section-title,
+h4.section-title {
+  display: flex;
+  align-items: center;
+  gap: 8px;
+  font-weight: 400;
+  padding: 5px 10px;
+  border-left: 3px solid var(--c-primary);
+  border-radius: 7px;
+  background: linear-gradient(180deg, #f4f8ff 0%, #edf3ff 100%);
+  color: #1e3a8a;
+  box-shadow: inset 0 0 0 1px #dbe7fb;
+}
+
 .mt-0 {
   margin-top: 0;
 }
@@ -2043,6 +2058,21 @@ details[open] > .sidebar__group-toggle .sidebar__toggle-arrow {
   gap: 8px;
 }
 
+.dm-carrier-select {
+  min-width: 140px;
+}
+
+.dm-service-wrap {
+  min-width: 200px;
+
+  .dm-inpost-panel,
+  .dm-apaczka-panel {
+    .form-control {
+      width: 100%;
+    }
+  }
+}
+
 .integration-settings-group {
   grid-column: 1 / -1;
   border: 1px solid var(--c-border);