Initial marketplace implementation

Full-stack marketplace for buying/selling second-hand items.
React 19 + TypeScript + Tailwind CSS v4 frontend with 17 screens,
Express + Prisma + Socket.io backend, Stripe payments, JWT auth.

Deployed at https://marketplace.173.212.212.157.sslip.io/

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

package.json

@@ -0,0 +1,13 @@
+{
+  "name": "marketplace",
+  "private": true,
+  "version": "1.0.0",
+  "workspaces": ["client", "server"],
+  "scripts": {
+    "dev": "npm run dev --workspace=client & npm run dev --workspace=server",
+    "dev:client": "npm run dev --workspace=client",
+    "dev:server": "npm run dev --workspace=server",
+    "build": "npm run build --workspace=client && npm run build --workspace=server",
+    "lint": "npm run lint --workspace=client"
+  }
+}