fix: bust CSS cache (v20260505b) + bump webapp to v1.7.2

style.css was still served with ?v=20260421a so all CSS changes since
April 21 (scale indicator redesign, banner close button fix, etc.) were
invisible in the kiosk WebView — it used the cached old file.

Bumping manifest.json version 1.7.1→1.7.2 causes the auto-update
detector (_checkWebappUpdate) to fire on the kiosk: it compares the
loaded page version (1.7.1) with the server version (1.7.2), detects
a change, and shows the '⬆️ Aggiorna' badge so the user can reload.

manifest.json

@@ -2,7 +2,7 @@
     "name": "EverShelf",
     "short_name": "EverShelf",
     "description": "Gestione completa della dispensa di casa con scansione barcode",
-    "version": "1.7.1",
+    "version": "1.7.2",
     "start_url": "/evershelf/",
     "display": "standalone",
     "background_color": "#f0f4e8",