feat: Add comprehensive backend validation, toast notifications, and Tokyo Night theme

- Backend: Add server-side validation with go-playground/validator/v10
- Frontend: Add toast notifications for API errors with @zerodevx/svelte-toast
- UI: Complete Tokyo Night theme redesign with modern animations
- Docs: Update COMPLETE_DOCUMENTATION.md and README.md with all enhancements
- Validation: Email format, password strength, and input sanitization
- UX: Real-time error feedback, loading states, and responsive design

backend/package.json

@@ -0,0 +1,16 @@
+{
+  "name": "backend",
+  "version": "1.0.0",
+  "main": "server.js",
+  "scripts": {
+    "start": "node server.js",
+    "dev": "node server.js"
+  },
+  "dependencies": {
+    "express": "^4.18.2",
+    "bcryptjs": "^2.4.3",
+    "jsonwebtoken": "^9.0.2",
+    "cors": "^2.8.5",
+    "body-parser": "^1.20.2"
+  }
+}