feat: asset usage audit plugin

Editor tool for the LA and 3D departments: which assets each level uses,
which are used nowhere, and export of a chosen set.

Three modules. AssetUsageAuditCore holds the whole analysis and links no
UI and no editor-only asset pipeline, so it stays runnable from a
commandlet; AssetUsageAuditEditor holds the Slate panel and everything
that needs UnrealEd or AssetTools; AssetUsageAuditTests holds 152 specs.

Load-bearing decisions, each of which produces a wrong answer if undone:

- Dependency queries are always Package + NoRequirements, never Hard. The
  map-to-external-actor edges the OFPA gatherer emits carry Game|Build
  without Hard, so a Hard query drops all 16117 external actor packages
  in this project. There is deliberately no Hard constant in the code.
- Crossing into another map is allowed only from a level or its external
  actor package. Without that rule WP_Main reported 18136 assets, of
  which 9994 belonged to L_MainLevel, reached through the GameMode.
- The verdict has five states, never a bool. The registry cannot see
  FMOD events, DataTable rows or string-built paths; those are Unknown,
  and the tool never proposes a deletion.
- Copying .uasset files does not preserve references - they are stored as
  full package paths. Only the Migrate layout produces something Unreal
  can open; the others write a manifest so the graph can be rebuilt.

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

Source/AssetUsageAuditEditor/Public/AssetUsageAuditEditorModule.h

@@ -0,0 +1,43 @@
+// NextGenium 2026. Asset Usage Audit.
+
+#pragma once
+
+#include "CoreMinimal.h"
+#include "Modules/ModuleManager.h"
+
+class IConsoleObject;
+class SDockTab;
+class FSpawnTabArgs;
+
+ASSETUSAGEAUDITEDITOR_API DECLARE_LOG_CATEGORY_EXTERN(LogAssetUsageAuditEditor, Log, All);
+
+/**
+ * Editor-side host: settings, console entry points and (from phase 3) the Slate panel.
+ *
+ * All analysis lives in AssetUsageAuditCore. This module only drives it and presents results,
+ * so a commandlet can reach exactly the same code path without dragging UI in.
+ */
+class FAssetUsageAuditEditorModule : public IModuleInterface
+{
+public:
+    virtual void StartupModule() override;
+    virtual void ShutdownModule() override;
+
+    /** Nomad tab id, also used as the invoke target from the Tools menu. */
+    static const FName PanelTabId;
+
+private:
+    void RegisterConsoleCommands();
+    void UnregisterConsoleCommands();
+
+    void RegisterTabSpawner();
+    void UnregisterTabSpawner();
+    void RegisterMenus();
+
+    TSharedRef<SDockTab> SpawnPanelTab(const FSpawnTabArgs& Args);
+
+    /** Shared implementation behind every console entry point. */
+    void ExecuteAudit(const TArray<FString>& Args, bool bOnlyUnused);
+
+    TArray<IConsoleObject*> ConsoleCommands;
+};