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.

database/migrations/20260308_000045_extend_apaczka_credentials.sql

@@ -0,0 +1,39 @@
+SET @sql = (
+    SELECT IF(
+        EXISTS (
+            SELECT 1
+            FROM information_schema.columns
+            WHERE table_schema = DATABASE()
+              AND table_name = 'apaczka_integration_settings'
+              AND column_name = 'app_id'
+        ),
+        'SELECT 1',
+        'ALTER TABLE apaczka_integration_settings ADD COLUMN app_id VARCHAR(128) NULL AFTER integration_id'
+    )
+);
+PREPARE stmt FROM @sql;
+EXECUTE stmt;
+DEALLOCATE PREPARE stmt;
+
+SET @sql = (
+    SELECT IF(
+        EXISTS (
+            SELECT 1
+            FROM information_schema.columns
+            WHERE table_schema = DATABASE()
+              AND table_name = 'apaczka_integration_settings'
+              AND column_name = 'app_secret_encrypted'
+        ),
+        'SELECT 1',
+        'ALTER TABLE apaczka_integration_settings ADD COLUMN app_secret_encrypted TEXT NULL AFTER app_id'
+    )
+);
+PREPARE stmt FROM @sql;
+EXECUTE stmt;
+DEALLOCATE PREPARE stmt;
+
+UPDATE apaczka_integration_settings
+SET app_secret_encrypted = api_key_encrypted
+WHERE (app_secret_encrypted IS NULL OR app_secret_encrypted = '')
+  AND api_key_encrypted IS NOT NULL
+  AND api_key_encrypted <> '';