feat: production-harden app and finalize merge-ready UX/theme baseline

- complete tokenized theme preset system and admin style guide visibility
- refine dashboard layout/scroll behavior and shared async/request UI states
- add user nav-visibility settings across API, migration, and frontend stores
- harden security headers/CSP handling and related test coverage
- enforce CI repository hygiene + frontend contract/theme/build quality gates
- update docs/env references and make migration smoke test head-aware

frontend/src/env.d.ts

@@ -1 +1,6 @@
 /// <reference types="vite/client" />
+
+declare module "@/theme/presets/*.js" {
+  const value: Record<string, unknown>;
+  export default value;
+}