test: comprehensive test suite for Manoon storefront

Add complete testing infrastructure with Vitest:

Testing Stack:
- Vitest for unit/integration tests
- @testing-library/react for component tests
- @playwright/test for E2E (installed, ready to configure)
- MSW for API mocking

Test Coverage:
1. Webhook Handler Tests (src/__tests__/integration/api/webhooks/saleor.test.ts)
   - ORDER_CONFIRMED: Emails + analytics
   - ORDER_CREATED: No duplicates
   - ORDER_FULFILLED: Tracking info
   - ORDER_CANCELLED: Cancellation reason
   - ORDER_FULLY_PAID: Payment confirmation
   - Error handling (400/500 responses)
   - Currency handling (RSD preservation)

2. OrderNotificationService Tests
   - Email sending in all 4 languages (SR, EN, DE, FR)
   - Price formatting verification
   - Admin vs Customer templates
   - Address formatting
   - Tracking info handling

3. AnalyticsService Tests
   - Revenue tracking with correct currency
   - Duplicate prevention verification
   - Error handling (doesn't break flow)
   - Singleton pattern

4. Utility Tests
   - formatPrice: RSD, EUR, USD formatting
   - Decimal and zero handling

Fixtures:
- Realistic order data in src/__tests__/fixtures/orders.ts
- Multiple scenarios (with tracking, cancelled, etc.)

Scripts:
- npm test: Run tests in watch mode
- npm run test:run: Run once
- npm run test:coverage: Generate coverage report
- npm run test:e2e: Run Playwright tests

Coverage target: 80%+ for critical paths

src/__tests__/unit/services/AnalyticsService.test.ts

@@ -0,0 +1,227 @@
+import { describe, it, expect, vi, beforeEach } from "vitest";
+
+// Mock OpenPanel before importing the service
+const mockTrack = vi.fn().mockResolvedValue(undefined);
+const mockRevenue = vi.fn().mockResolvedValue(undefined);
+
+vi.mock("@openpanel/nextjs", () => ({
+  OpenPanel: vi.fn().mockImplementation(() => ({
+    track: mockTrack,
+    revenue: mockRevenue,
+  })),
+}));
+
+// Import after mock is set up
+import { analyticsService } from "@/lib/services/AnalyticsService";
+
+describe("AnalyticsService", () => {
+  beforeEach(() => {
+    vi.clearAllMocks();
+  });
+
+  describe("trackOrderReceived", () => {
+    it("should track order with all details", async () => {
+      await analyticsService.trackOrderReceived({
+        orderId: "order-123",
+        orderNumber: "1524",
+        total: 5479,
+        currency: "RSD",
+        itemCount: 3,
+        customerEmail: "test@example.com",
+        eventType: "ORDER_CONFIRMED",
+      });
+
+      expect(mockTrack).toHaveBeenCalledWith("order_received", {
+        order_id: "order-123",
+        order_number: "1524",
+        total: 5479,
+        currency: "RSD",
+        item_count: 3,
+        customer_email: "test@example.com",
+        event_type: "ORDER_CONFIRMED",
+      });
+    });
+
+    it("should handle large order values", async () => {
+      await analyticsService.trackOrderReceived({
+        orderId: "order-456",
+        orderNumber: "2000",
+        total: 500000, // Large amount
+        currency: "RSD",
+        itemCount: 100,
+        customerEmail: "bulk@example.com",
+        eventType: "ORDER_CONFIRMED",
+      });
+
+      expect(mockTrack).toHaveBeenCalledWith(
+        "order_received",
+        expect.objectContaining({
+          total: 500000,
+          item_count: 100,
+        })
+      );
+    });
+
+    it("should not throw if tracking fails", async () => {
+      mockTrack.mockRejectedValueOnce(new Error("Network error"));
+
+      await expect(
+        analyticsService.trackOrderReceived({
+          orderId: "order-123",
+          orderNumber: "1524",
+          total: 1000,
+          currency: "RSD",
+          itemCount: 1,
+          customerEmail: "test@example.com",
+          eventType: "ORDER_CONFIRMED",
+        })
+      ).resolves.not.toThrow();
+    });
+  });
+
+  describe("trackRevenue", () => {
+    it("should track revenue with correct currency", async () => {
+      await analyticsService.trackRevenue({
+        amount: 5479,
+        currency: "RSD",
+        orderId: "order-123",
+        orderNumber: "1524",
+      });
+
+      expect(mockRevenue).toHaveBeenCalledWith(5479, {
+        currency: "RSD",
+        order_id: "order-123",
+        order_number: "1524",
+      });
+    });
+
+    it("should track revenue with different currencies", async () => {
+      // Test EUR
+      await analyticsService.trackRevenue({
+        amount: 100,
+        currency: "EUR",
+        orderId: "order-1",
+        orderNumber: "1000",
+      });
+
+      expect(mockRevenue).toHaveBeenCalledWith(100, {
+        currency: "EUR",
+        order_id: "order-1",
+        order_number: "1000",
+      });
+
+      // Test USD
+      await analyticsService.trackRevenue({
+        amount: 150,
+        currency: "USD",
+        orderId: "order-2",
+        orderNumber: "1001",
+      });
+
+      expect(mockRevenue).toHaveBeenCalledWith(150, {
+        currency: "USD",
+        order_id: "order-2",
+        order_number: "1001",
+      });
+    });
+
+    it("should log tracking for debugging", async () => {
+      const consoleSpy = vi.spyOn(console, "log").mockImplementation(() => {});
+
+      await analyticsService.trackRevenue({
+        amount: 5479,
+        currency: "RSD",
+        orderId: "order-123",
+        orderNumber: "1524",
+      });
+
+      expect(consoleSpy).toHaveBeenCalledWith(
+        "Tracking revenue: 5479 RSD for order 1524"
+      );
+
+      consoleSpy.mockRestore();
+    });
+
+    it("should not throw if revenue tracking fails", async () => {
+      mockRevenue.mockRejectedValueOnce(new Error("API error"));
+
+      await expect(
+        analyticsService.trackRevenue({
+          amount: 1000,
+          currency: "RSD",
+          orderId: "order-123",
+          orderNumber: "1524",
+        })
+      ).resolves.not.toThrow();
+    });
+
+    it("should handle zero amount orders", async () => {
+      await analyticsService.trackRevenue({
+        amount: 0,
+        currency: "RSD",
+        orderId: "order-000",
+        orderNumber: "0000",
+      });
+
+      expect(mockRevenue).toHaveBeenCalledWith(0, {
+        currency: "RSD",
+        order_id: "order-000",
+        order_number: "0000",
+      });
+    });
+  });
+
+  describe("track", () => {
+    it("should track custom events", async () => {
+      await analyticsService.track("custom_event", {
+        property1: "value1",
+        property2: 123,
+      });
+
+      expect(mockTrack).toHaveBeenCalledWith("custom_event", {
+        property1: "value1",
+        property2: 123,
+      });
+    });
+
+    it("should not throw on tracking errors", async () => {
+      mockTrack.mockRejectedValueOnce(new Error("Tracking failed"));
+
+      await expect(
+        analyticsService.track("test_event", { test: true })
+      ).resolves.not.toThrow();
+    });
+  });
+
+  describe("Singleton pattern", () => {
+    it("should return the same instance", () => {
+      // Import fresh to test singleton
+      const { analyticsService: service1 } = require("@/lib/services/AnalyticsService");
+      const { analyticsService: service2 } = require("@/lib/services/AnalyticsService");
+
+      expect(service1).toBe(service2);
+    });
+  });
+
+  describe("Error handling", () => {
+    it("should log errors but not throw", async () => {
+      const consoleErrorSpy = vi.spyOn(console, "error").mockImplementation(() => {});
+      mockTrack.mockRejectedValueOnce(new Error("Test error"));
+
+      await analyticsService.trackOrderReceived({
+        orderId: "order-123",
+        orderNumber: "1524",
+        total: 1000,
+        currency: "RSD",
+        itemCount: 1,
+        customerEmail: "test@example.com",
+        eventType: "ORDER_CONFIRMED",
+      });
+
+      expect(consoleErrorSpy).toHaveBeenCalled();
+      expect(consoleErrorSpy.mock.calls[0][0]).toContain("Failed to track order received");
+
+      consoleErrorSpy.mockRestore();
+    });
+  });
+});