feat: add catalog audit page

Checks for:
- items_base entries without catalog_items (not purchasable)
- catalog_items referencing non-existent items_base
- Items without .nitro or icon files on disk
- Duplicate classnames
- Items missing from all configured clone sources

src/app/api/admin/import/audit/route.ts

@@ -0,0 +1,13 @@
+import { withAdmin } from "@/lib/api-handler";
+import { apiError, apiOk } from "@/lib/api-response";
+import { PERMS } from "@/lib/permissions";
+import { runCatalogAudit } from "@/lib/services/catalog-audit";
+
+export const POST = withAdmin({ permission: PERMS.ASSETS_IMPORT }, async () => {
+	try {
+		const result = await runCatalogAudit();
+		return apiOk(result as unknown as Record<string, unknown>);
+	} catch (err) {
+		return apiError(`Audit failed: ${(err as Error).message}`, 500);
+	}
+});