Complete migration to @spree/next package (#7)

* Complete migration to @spree/next package

Migrate all server-side data layer from direct @spree/sdk usage to @spree/next, which provides Server Actions for authentication, cart, checkout, and customer operations with built-in cookie-based auth and token refresh.

Changes:
- Add @spree/next@0.1.1 as dependency and configure transpilePackages
- Delete src/lib/spree.ts (client initialization now internal to @spree/next)
- Delete src/lib/data/auth-request.ts (token refresh now internal to @spree/next)
- Simplify src/lib/data/cookies.ts to only isAuthenticated() check
- Rewrite all data layer files to delegate to @spree/next Server Actions
- Fix React 19 hook ordering in CheckoutPage (use() before other hooks)
- Fix nested form issue in AddressStep component

Result: Reduced data layer from 867 to 252 lines while maintaining all functionality.

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

* Fix inconsistent error handling in cart and add return type to getCreditCards

Wrap addToCart, updateCartItem, removeCartItem in try/catch with structured
{ success, cart, error } returns for consistency with associateCartWithUser.
Update CartContext to handle the new structured return type. Add explicit
return type annotation to getCreditCards.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* Wrap clearCart in structured error handling for consistency

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* Add Vitest test suite and GitHub Actions CI

Set up Vitest with React Testing Library and jsdom for unit/integration
testing. Add 58 tests across 5 test files covering the data layer (cart,
checkout, customer), CartContext, and ProductCard component. Add GitHub
Actions CI workflow with parallel lint, typecheck, and test jobs.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* Fix Biome lint errors in test files and vitest config

Use node: protocol for path import, fix import ordering, and auto-format.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

---------

Co-authored-by: Claude Haiku 4.5 <noreply@anthropic.com>

Author: damianlegawiec

.github/workflows/ci.yml

@@ -0,0 +1,48 @@
+name: CI
+
+on:
+  push:
+    branches: [main]
+  pull_request:
+    branches: [main]
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
+jobs:
+  lint:
+    name: Lint
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-node@v4
+        with:
+          node-version: 20
+          cache: npm
+      - run: npm ci
+      - run: npm run check
+
+  typecheck:
+    name: Type Check
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-node@v4
+        with:
+          node-version: 20
+          cache: npm
+      - run: npm ci
+      - run: npx tsc --noEmit
+
+  test:
+    name: Unit Tests
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-node@v4
+        with:
+          node-version: 20
+          cache: npm
+      - run: npm ci
+      - run: npm run test

next.config.ts

@@ -1,6 +1,7 @@
 import type { NextConfig } from "next";
 
 const nextConfig: NextConfig = {
+  transpilePackages: ["@spree/next", "@spree/sdk"],
   images: {
     qualities: [25, 50, 75, 100],
     dangerouslyAllowLocalIP: true, // Allow localhost images in development