feat: add GitHub OAuth2 login and protect product mutations with JWT

- add /auth/login and /auth/callback (rewritten to pages/api/auth/*) for the
  GitHub Authorization Code flow, with a state cookie against login CSRF
- issue a 1h JWT after the code exchange and verify it (HS256) in the Apollo
  context; createProduct, updateProduct and deleteProduct require it
- set products.created_by from the logged-in GitHub user (upsert into users)
- preset the Authorization header in the embedded Sandbox
- add jsonwebtoken, drop unused cors, rename package to week-7

pages/index.js

@@ -15,6 +15,8 @@ function Home() {
         target: '#embedded-sandbox',
         initialEndpoint: `${window.location.origin}/api/graphql`,
         initialState: {
+          // Ganti <paste-token-here> dengan JWT dari /auth/login supaya mutation diizinkan.
+          headers: { Authorization: 'Bearer <paste-token-here>' },
           document: `query TestCategoriesWithProducts {
   categories {
     id
@@ -44,7 +46,7 @@ function Home() {
     React.createElement(
       Head,
       null,
-      React.createElement('title', null, 'GraphQL Sandbox - Lab 04')
+      React.createElement('title', null, 'GraphQL Sandbox')
     ),
     React.createElement('div', {
       id: 'embedded-sandbox',