feat: Implement Phase 1 Shopify-inspired settings (Store, Payments, Shipping)

✨ Features:
- Store Details page with live currency preview
- Payments page with visual provider cards and test mode
- Shipping & Delivery page with zone cards and local pickup
- Shared components: SettingsLayout, SettingsCard, SettingsSection, ToggleField

🎨 UI/UX:
- Card-based layouts (not boring forms)
- Generous whitespace and visual hierarchy
- Toast notifications using sonner (reused from Orders)
- Sticky save button at top
- Mobile-responsive design

🔧 Technical:
- Installed ESLint with TypeScript support
- Fixed all lint errors (0 errors)
- Phase 1 files have zero warnings
- Used existing toast from sonner (not reinvented)
- Updated routes in App.tsx

📝 Files Created:
- Store.tsx (currency preview, address, timezone)
- Payments.tsx (provider cards, manual methods)
- Shipping.tsx (zone cards, rates, local pickup)
- SettingsLayout.tsx, SettingsCard.tsx, SettingsSection.tsx, ToggleField.tsx

Phase 1 complete: 18-24 hours estimated work

admin-spa/src/components/nav/SubmenuBar.tsx

@@ -5,11 +5,12 @@ import type { SubItem } from '@/nav/tree';
 type Props = { items?: SubItem[] };
 
 export default function SubmenuBar({ items = [] }: Props) {
+  // Always call hooks first
+  const { pathname } = useLocation();
+  
   // Single source of truth: props.items. No fallbacks, no demos, no path-based defaults
   if (items.length === 0) return null;
 
-  const { pathname } = useLocation();
-
   return (
     <div data-submenubar className="border-b border-border bg-background/95">
       <div className="px-4 py-2">