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>

packages/convex/src/index.ts

@@ -0,0 +1 @@
+export { ConvexClientProvider } from "./provider";

packages/convex/src/provider.tsx

@@ -0,0 +1,20 @@
+"use client";
+
+import { ReactNode } from "react";
+import { ConvexReactClient } from "convex/react";
+import { ConvexProviderWithClerk } from "convex/react-clerk";
+import { useAuth } from "@clerk/nextjs";
+
+if (!process.env.NEXT_PUBLIC_CONVEX_URL) {
+  throw new Error("Missing NEXT_PUBLIC_CONVEX_URL");
+}
+
+const convex = new ConvexReactClient(process.env.NEXT_PUBLIC_CONVEX_URL);
+
+export function ConvexClientProvider({ children }: { children: ReactNode }) {
+  return (
+    <ConvexProviderWithClerk client={convex} useAuth={useAuth}>
+      {children}
+    </ConvexProviderWithClerk>
+  );
+}