fix(qr): guest menu 500 (SSR) + remove café discovery from owner panel

1. The /q/{code} guest menu returned HTTP 500 on every load. Root cause:
   menu-item-model-viewer.tsx did a top-level `import "@google/model-viewer"`,
   a browser-only lib that touches `self` at module evaluation. Next pulled
   it into the server module graph (page → qr-guest-menu → qr-menu-3d-sheet →
   model-viewer) and SSR crashed with "self is not defined". Now the library
   is imported lazily inside useEffect (client-only); a poster placeholder
   shows until the custom element registers. Verified /q/* now returns 200.

2. Removed the "discover" (browse other cafés) item from the café owner
   sidebar — café discovery belongs in Koja, not the owner panel. The owner
   still manages their OWN Koja listing from Settings.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

web/dashboard/src/lib/sidebar-nav.ts

@@ -21,7 +21,6 @@ import {
   Wallet,
   Clock,
   LifeBuoy,
-  Compass,
 } from "lucide-react";
 
 export type NavGroupId = "main" | "customers" | "management";
@@ -39,7 +38,6 @@ export type NavItemKey =
   | "coupons"
   | "sms"
   | "reviews"
-  | "discover"
   | "inventory"
   | "expenses"
   | "shifts"
@@ -93,7 +91,8 @@ export const NAV_GROUPS: NavGroupDef[] = [
       { key: "coupons", href: "/coupons", icon: Ticket },
       { key: "sms", href: "/sms", icon: MessageSquare },
       { key: "reviews", href: "/reviews", icon: Star },
-      { key: "discover", href: "/discover", icon: Compass },
+      // NOTE: café discovery (browsing other cafés) lives in Koja, not the owner
+      // panel. The owner manages their OWN Koja listing from Settings.
     ],
   },
   {