Polish explorer frontend validation and utility pages

docs/EXPLORER_API_ACCESS.md

@@ -28,6 +28,19 @@ Why:
 - Setting `NEXT_PUBLIC_API_URL=https://explorer.d-bis.org/api` will incorrectly produce requests like `/api/api/v2/*`.
 - Token aggregation remains under `/token-aggregation/api/v1/*` and is linked separately by the frontend.
 
+### Local frontend validation
+
+From `frontend/`, the current local validation flow is:
+
+```bash
+npm run build:check
+BASE_URL=http://127.0.0.1:3000 npm run smoke:routes
+```
+
+- `build:check` runs lint, type-check, and a production build.
+- `smoke:routes` performs a lightweight route and content sweep against a running frontend instance.
+- `npm run dev` now binds to `127.0.0.1` by default, but still honors `HOST` and `PORT` overrides.
+
 ---
 
 ## CSP blocks eval / “script-src blocked”