feat: initial commit — storefront, convex backend, and shared packages

Completes the first milestone of The Pet Loft ecommerce platform:
- apps/storefront: full customer-facing Next.js app with HeroUI (cart,
  checkout, orders, wishlist, product detail, shop, search, auth)
- convex/: serverless backend with schema, queries, mutations, actions,
  HTTP routes, Stripe/Shippo integrations, and co-located tests
- packages/types, packages/utils, packages/convex: shared workspace packages

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

apps/storefront/next.config.js

@@ -0,0 +1,8 @@
+/** @type {import('next').NextConfig} */
+const nextConfig = {
+  transpilePackages: ["@repo/convex", "@repo/types", "@repo/utils"],
+  // PPR: enable when using Next.js canary. Uncomment and add experimental_ppr to PDP page:
+  // experimental: { ppr: "incremental" },
+};
+
+module.exports = nextConfig;