feat: Coupons CRUD - Frontend list page (Phase 2)

Implemented complete Coupons list page following PROJECT_SOP.md

Created: CouponsApi helper (lib/api/coupons.ts)
- TypeScript interfaces for Coupon and CouponFormData
- Full CRUD methods: list, get, create, update, delete
- Pagination and filtering support

Updated: Coupons/index.tsx (Complete rewrite)
- Full CRUD list page with SOP-compliant UI
- Toolbar with bulk actions and filters
- Desktop table + Mobile cards (responsive)
- Pagination support
- Search and filter by discount type

Following PROJECT_SOP.md Standards:
✅ Toolbar pattern: Bulk delete, Refresh (REQUIRED), Filters
✅ Table UI: p-3 padding, hover:bg-muted/30, bg-muted/50 header
✅ Button styling: bg-red-600 for delete, inline-flex gap-2
✅ Reset filters: Text link style (NOT button)
✅ Empty state: Icon + message + helper text
✅ Mobile responsive: Cards with md:hidden
✅ Error handling: ErrorCard for page loads
✅ Loading state: LoadingState component
✅ FAB configuration: Navigate to /coupons/new

Features:
- Bulk selection with checkbox
- Bulk delete with confirmation
- Search by coupon code
- Filter by discount type
- Pagination (prev/next)
- Formatted discount amounts
- Usage tracking display
- Expiry date display
- Edit navigation

UI Components Used:
- Card, Input, Select, Checkbox, Badge
- Lucide icons: Trash2, RefreshCw, Edit, Tag
- Consistent spacing and typography

Next Steps:
- Create New.tsx (create coupon form)
- Create Edit.tsx (edit coupon form)
- Update NavigationRegistry.php
- Update API_ROUTES.md

admin-spa/src/lib/api/coupons.ts

@@ -0,0 +1,95 @@
+import { api } from '../api';
+
+export interface Coupon {
+  id: number;
+  code: string;
+  amount: number;
+  discount_type: 'percent' | 'fixed_cart' | 'fixed_product';
+  description: string;
+  usage_count: number;
+  usage_limit: number | null;
+  date_expires: string | null;
+  individual_use?: boolean;
+  product_ids?: number[];
+  excluded_product_ids?: number[];
+  usage_limit_per_user?: number | null;
+  limit_usage_to_x_items?: number | null;
+  free_shipping?: boolean;
+  product_categories?: number[];
+  excluded_product_categories?: number[];
+  exclude_sale_items?: boolean;
+  minimum_amount?: number | null;
+  maximum_amount?: number | null;
+  email_restrictions?: string[];
+}
+
+export interface CouponListResponse {
+  coupons: Coupon[];
+  total: number;
+  page: number;
+  per_page: number;
+  total_pages: number;
+}
+
+export interface CouponFormData {
+  code: string;
+  amount: number;
+  discount_type: 'percent' | 'fixed_cart' | 'fixed_product';
+  description?: string;
+  date_expires?: string | null;
+  individual_use?: boolean;
+  product_ids?: number[];
+  excluded_product_ids?: number[];
+  usage_limit?: number | null;
+  usage_limit_per_user?: number | null;
+  limit_usage_to_x_items?: number | null;
+  free_shipping?: boolean;
+  product_categories?: number[];
+  excluded_product_categories?: number[];
+  exclude_sale_items?: boolean;
+  minimum_amount?: number | null;
+  maximum_amount?: number | null;
+  email_restrictions?: string[];
+}
+
+export const CouponsApi = {
+  /**
+   * List coupons with pagination and filtering
+   */
+  list: async (params?: {
+    page?: number;
+    per_page?: number;
+    search?: string;
+    discount_type?: string;
+  }): Promise<CouponListResponse> => {
+    return api.get('/coupons', { params });
+  },
+
+  /**
+   * Get single coupon
+   */
+  get: async (id: number): Promise<Coupon> => {
+    return api.get(`/coupons/${id}`);
+  },
+
+  /**
+   * Create new coupon
+   */
+  create: async (data: CouponFormData): Promise<Coupon> => {
+    return api.post('/coupons', data);
+  },
+
+  /**
+   * Update coupon
+   */
+  update: async (id: number, data: Partial<CouponFormData>): Promise<Coupon> => {
+    return api.put(`/coupons/${id}`, data);
+  },
+
+  /**
+   * Delete coupon
+   */
+  delete: async (id: number, force: boolean = false): Promise<{ success: boolean; id: number }> => {
+    return api.del(`/coupons/${id}?force=${force ? 'true' : 'false'}`);
+  },
+};