feat(web): privacy-first cookie banner

- New CookieBanner client component anchored at the bottom of the locale
  layout, dismissed via Button click and persisted via localStorage key
  ketopath:cookie-notice-ack (no cookie set for the dismissal itself)
- Italian copy: only essential cookies for authentication/session, no
  analytics or third-party trackers (consistent with the ADR 0001 stance
  and CLAUDE.md "Privacy first" non-negotiable)
- Layout body now uses bg-background / text-foreground tokens so dark mode
  toggling will work the day we add it

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

apps/web/messages/it.json

@@ -9,6 +9,11 @@
     "signOut": "Esci",
     "completeProfile": "Completa il tuo profilo"
   },
+  "CookieBanner": {
+    "aria": "Informativa cookie",
+    "message": "Usiamo solo cookie essenziali per l'autenticazione e la sessione. Niente analytics o tracker di terze parti.",
+    "dismiss": "Ho capito"
+  },
   "Metadata": {
     "title": "KetoPath — Chetogenica e digiuno intermittente personalizzati",
     "description": "Web app italiana per la gestione strutturata di chetogenica e digiuno intermittente, con piani adattivi, tracking e lista della spesa automatica."