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>

.gitignore

@@ -0,0 +1,33 @@
+# Dependencies
+node_modules
+.pnp
+.pnp.js
+
+# Build outputs
+.next
+dist
+build
+out
+
+# Turbo
+.turbo
+
+# Environment variables
+.env
+.env.local
+.env.development.local
+.env.test.local
+.env.production.local
+
+# Misc
+.DS_Store
+*.pem
+npm-debug.log*
+yarn-debug.log*
+yarn-error.log*
+
+# TypeScript
+*.tsbuildinfo
+
+# Convex
+convex/_generated