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/routes/Settings/components/SettingsSection.tsx

@@ -0,0 +1,31 @@
+import React from 'react';
+import { Label } from '@/components/ui/label';
+
+interface SettingsSectionProps {
+  label: string;
+  description?: string;
+  required?: boolean;
+  children: React.ReactNode;
+  htmlFor?: string;
+}
+
+export function SettingsSection({
+  label,
+  description,
+  required = false,
+  children,
+  htmlFor,
+}: SettingsSectionProps) {
+  return (
+    <div className="space-y-2">
+      <Label htmlFor={htmlFor} className="text-sm font-medium">
+        {label}
+        {required && <span className="text-destructive ml-1">*</span>}
+      </Label>
+      {description && (
+        <p className="text-sm text-muted-foreground">{description}</p>
+      )}
+      <div>{children}</div>
+    </div>
+  );
+}