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/AssetUsageAuditSettings.h

@@ -0,0 +1,90 @@
+// NextGenium 2026. Asset Usage Audit.
+
+#pragma once
+
+#include "CoreMinimal.h"
+#include "AssetUsageAuditTypes.h"
+#include "Engine/DeveloperSettings.h"
+#include "AssetUsageAuditSettings.generated.h"
+
+/**
+ * Team-shared configuration, written to Config/DefaultEditor.ini.
+ *
+ * That file is Perforce-tracked (only Plugins/** is p4-ignored), so the exclusion list and the
+ * type presets are reviewable and shared. Per-user state - last filter, column layout - belongs
+ * in UAssetUsageAuditUserSettings instead, which stays in Saved/Config.
+ */
+UCLASS(config = Editor, defaultconfig, meta = (DisplayName = "Asset Usage Audit"))
+class ASSETUSAGEAUDITEDITOR_API UAssetUsageAuditSettings : public UDeveloperSettings
+{
+    GENERATED_BODY()
+
+public:
+    UAssetUsageAuditSettings();
+
+    /** Default folder for exported files and reports. Empty means <Project>/Saved/AssetUsageAudit. */
+    UPROPERTY(config, EditAnywhere, Category = "Export", meta = (ToolTip = "Default destination for exported assets and reports. Leave empty to use Saved/AssetUsageAudit."))
+    FString DefaultExportDirectory;
+
+    /** Overwrite existing files on export, or add/increment a numeric suffix. */
+    UPROPERTY(config, EditAnywhere, Category = "Export", meta = (ToolTip = "When a file of the same name already exists: replace it, or write Foo_1, Foo_2 and so on."))
+    bool bOverwriteExistingFiles = false;
+
+    /**
+     * Asset class short name -> interchange file extension, used by the "Convert" export mode.
+     *
+     * Empty falls back to the built-in table. Lookup follows the class hierarchy, so one entry for
+     * MaterialInterface would cover every material instance. Only add a class the engine ships a
+     * UExporter for: an entry with no exporter behind it produces no file and reads as a bug.
+     */
+    UPROPERTY(config, EditAnywhere, Category = "Export", meta = (ToolTip = "Which file format each asset class converts to, e.g. StaticMesh -> fbx. Leave empty for the built-in defaults."))
+    TMap<FString, FString> ExchangeFormatByClass;
+
+    /**
+     * How exported files are arranged under the destination.
+     *
+     * Replaced an earlier bMirrorFolderStructure boolean. Adding "one folder per asset" as a second
+     * boolean would have made "mirror the tree AND a folder per asset" expressible, and it means
+     * nothing - the enum makes the three arrangements mutually exclusive, which they are.
+     */
+    UPROPERTY(config, EditAnywhere, Category = "Export", meta = (ToolTip = "Flat: every file side by side. Mirror: recreate the /Game tree. Folder per asset: each ticked asset gets its own folder with its dependencies beside it."))
+    EExportLayout ExportLayout = EExportLayout::Flat;
+
+    /**
+     * Within each asset's folder, sort its dependencies into per-type subfolders.
+     *
+     * Only has an effect with the folder-per-asset layout - the other two have no per-asset folder
+     * to sort inside. Folder names come from the same type presets the Types filter shows, so the
+     * folders match the words used to filter.
+     */
+    UPROPERTY(config, EditAnywhere, Category = "Export", meta = (EditCondition = "ExportLayout == EExportLayout::FolderPerAsset", ToolTip = "Put textures, materials and meshes into their own subfolders inside each asset's folder."))
+    bool bGroupDependenciesByType = false;
+
+    /**
+     * Package or content-relative prefixes excluded from the sweep.
+     *
+     * Defaults cover this project's bought content packs. Roughly 65% of the project's assets are
+     * third-party, so without this the report is dominated by content nobody audits.
+     */
+    UPROPERTY(config, EditAnywhere, Category = "Filtering", meta = (ToolTip = "Folders to skip entirely. Accepts /Game/... or Content/... form."))
+    TArray<FString> ExcludedPackagePaths;
+
+    /** Roots to sweep. Empty means /Game. */
+    UPROPERTY(config, EditAnywhere, Category = "Filtering", meta = (ToolTip = "Folders to analyse. Leave empty to sweep all of /Game."))
+    TArray<FString> IncludedPackagePaths;
+
+    /** Read Config/ and Source/ for path literals the Asset Registry cannot see. */
+    UPROPERTY(config, EditAnywhere, Category = "Filtering", meta = (ToolTip = "Scan Config/ and Source/ for /Game paths. Without this the project's GameMode and GameInstance report as unused, because only DefaultEngine.ini names them."))
+    bool bScanIndirectReferences = true;
+
+    /** Hide __ExternalActors__ / __ExternalObjects__ rows; they are plumbing, not artist-facing. */
+    UPROPERTY(config, EditAnywhere, Category = "Filtering", meta = (ToolTip = "Hide One File Per Actor packages from the results. They are still traversed."))
+    bool bHideExternalPackages = true;
+
+    static const UAssetUsageAuditSettings* Get();
+
+    /** Resolved absolute export directory, applying the Saved/AssetUsageAudit fallback. */
+    FString GetResolvedExportDirectory() const;
+
+    virtual FName GetCategoryName() const override;
+};