feat(offline): full offline mode — cache sync, write queue, startup recovery

- Full-screen network error overlay (z-index 300000, above screensaver)
- 'Continue offline' button after 3s, auto-enter after 8s
- Inventory + settings synced to localStorage at startup (during health check)
- inventory_summary and stats computed from local cache while offline
- Write queue (add/use/update/delete): optimistic UI + sync on reconnect
- Pending ops survive page refresh — detected and re-synced at next startup
- Buffered remoteLog/reportError flushed to server (GitHub issues) on restore
- AI/network sections hidden in offline mode (CSS body.offline-mode)
- Banner: pulsing dot while loading cache, item count when ready
- Broken external images replaced with grey SVG placeholder
- Fix: opened items marked is_edible:true offline (was flooding banner)
- Fix: _semverGt() prevents update badge for older GitHub releases
- Bump version to v1.7.25

manifest.json

@@ -2,7 +2,7 @@
     "name": "EverShelf",
     "short_name": "EverShelf",
     "description": "Gestione completa della dispensa di casa con scansione barcode",
-    "version": "1.7.24",
+    "version": "1.7.25",
     "start_url": "/evershelf/",
     "display": "standalone",
     "background_color": "#f0f4e8",