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>

turbo.json

@@ -0,0 +1,21 @@
+{
+  "$schema": "https://turbo.build/schema.json",
+  "ui": "tui",
+  "tasks": {
+    "build": {
+      "dependsOn": ["^build"],
+      "inputs": ["$TURBO_DEFAULT$", ".env*"],
+      "outputs": [".next/**", "!.next/cache/**", "dist/**"]
+    },
+    "dev": {
+      "cache": false,
+      "persistent": true
+    },
+    "lint": {
+      "dependsOn": ["^lint"]
+    },
+    "type-check": {
+      "dependsOn": ["^build"]
+    }
+  }
+}