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>

client/src/index.css

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+@import "tailwindcss";
+
+@theme {
+  --font-sans: 'Inter', sans-serif;
+
+  --color-primary-50: #f5f3ff;
+  --color-primary-100: #ede9fe;
+  --color-primary-200: #ddd6fe;
+  --color-primary-300: #c4b5fd;
+  --color-primary-400: #a78bfa;
+  --color-primary-500: #8b5cf6;
+  --color-primary-600: #7c3aed;
+  --color-primary-700: #6d28d9;
+  --color-primary-800: #5b21b6;
+  --color-primary-900: #4c1d95;
+
+  --color-pink-400: #f472b6;
+  --color-pink-500: #ec4899;
+  --color-pink-600: #db2777;
+
+  --color-accent: #E994B8;
+
+  --color-surface: #ffffff;
+  --color-background: #f3f0ff;
+  --color-text: #1f2937;
+  --color-text-secondary: #6b7280;
+  --color-border: #e5e7eb;
+  --color-success: #10b981;
+  --color-error: #ef4444;
+  --color-warning: #f59e0b;
+}
+
+* {
+  box-sizing: border-box;
+}
+
+body {
+  margin: 0;
+  background: var(--color-background);
+  color: var(--color-text);
+  font-family: 'Inter', sans-serif;
+  min-height: 100vh;
+}
+
+::-webkit-scrollbar {
+  width: 6px;
+  height: 6px;
+}
+::-webkit-scrollbar-track {
+  background: transparent;
+}
+::-webkit-scrollbar-thumb {
+  background: var(--color-border);
+  border-radius: 3px;
+}