feat: import assets from an external folder

Reverse direction of the export: read a folder of .uasset files, recover
each one's original package path, and bring the chosen ones back.

Recovering the path is the hard part - a reference inside a .uasset names
its target by full package path, so a file only works when restored to
where it came from. Four sources are tried and the one used is shown per
row: our manifest, the package header, the folder structure, or nothing.

The package header carries the name on this project's assets, measured,
so a flat export without a manifest still restores correctly. The engine
notes the field is not always written, hence the chain rather than one
check.

Import refuses to destroy work: existing assets are skipped unless
overwrite is explicitly on, and a package loaded in the editor is never
replaced.

Also verifies Migrate on real data for the first time - asset and its
dependency land at the correct package paths.

Co-Authored-By: Claude Code <noreply@anthropic.com>

Source/AssetUsageAuditEditor/Private/AssetUsageAuditEditorModule.cpp

@@ -5,6 +5,7 @@
 #include "AssetUsageAuditSettings.h"
 #include "AssetUsageAuditor.h"
 #include "AssetUsageReportWriter.h"
+#include "SAssetImportDialog.h"
 #include "SAssetUsageAuditPanel.h"
 #include "AssetRegistry/AssetRegistryModule.h"
 #include "AssetRegistry/IAssetRegistry.h"
@@ -90,6 +91,18 @@ void FAssetUsageAuditEditorModule::RegisterMenus()
         {
             FGlobalTabmanager::Get()->TryInvokeTab(FAssetUsageAuditEditorModule::PanelTabId);
         })));
+
+    // Import sits beside the audit rather than inside its panel: it is the reverse direction and
+    // needs no audit result, so requiring a sweep first would be pure ceremony.
+    Section.AddMenuEntry(
+        TEXT("ImportAssetsFromFolder"),
+        LOCTEXT("OpenImport", "Import Assets from Folder..."),
+        LOCTEXT("OpenImportTip", "Read a folder of exported .uasset files and bring the chosen ones back into this project."),
+        FSlateIcon(FAppStyle::GetAppStyleSetName(), "Icons.Import"),
+        FUIAction(FExecuteAction::CreateLambda([]()
+        {
+            ShowAssetImportDialog();
+        })));
 }
 
 void FAssetUsageAuditEditorModule::RegisterConsoleCommands()