iEduPortal PWA — Stage 58

Stage 58 improves the offline recovery experience without changing the database or API.

Changes:
- Service-worker cache version v10.
- Offline page now provides a clear retry action.
- Offline page detects connection restoration and automatically retries.
- Existing 5-second network timeout remains in place for navigation.
- Navigation still falls back to the cached public PWA shell, then the offline page.
- Existing background sync, update lifecycle, accessibility/mobile UX and storage diagnostics remain intact.
- API and authenticated/private application routes remain excluded from PWA caching.
