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>

convex/auth.config.ts

@@ -0,0 +1,10 @@
+import { AuthConfig } from "convex/server";
+
+export default {
+  providers: [
+    {
+      domain: process.env.CLERK_STOREFRONT_JWT_ISSUER_DOMAIN!,
+      applicationID: "convex",
+    },
+  ],
+} satisfies AuthConfig;