feat: implement complete auth/registration system (backend + frontend)

Backend: Add Express 5 API layer with Auth, User, Helper, Medical, and Location
modules. Each module has service (business logic with field whitelisting),
controller (HTTP layer), routes (with express-validator), and utilities.
Includes shared ApiError/ApiResponse/asyncHandler/validate middleware.

Frontend: Add Redux Toolkit store with auth slice (17 reducers), API client
with Axios interceptors, and 5 multi-step signup screens (StepOne role selector,
StepTwoUser emergency contacts, StepTwoHelper skills/availability,
StepThreeMedical optional health info, StepLocation GPS/manual address).
Includes FormInput, PrimaryButton, StepIndicator shared components.

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

Author: MStarRobotics

LifeLine-Backend/package.json

@@ -1,16 +1,24 @@
 {
   "name": "LifeLine-Backend",
   "version": "1.0.0",
-  "description": "",
-  "main": "index.js",
+  "description": "LifeLine Emergency Response Backend API",
+  "main": "src/server.mjs",
+  "type": "module",
   "scripts": {
-    "test": "echo \"Error: no test specified\" && exit 1"
+    "start": "node src/server.mjs",
+    "dev": "node --watch src/server.mjs",
+    "test": "node tests/api.test.mjs",
+    "test:watch": "node --watch tests/api.test.mjs"
   },
   "keywords": [],
   "author": "",
   "license": "ISC",
   "packageManager": "pnpm@10.28.2",
   "dependencies": {
+    "cors": "^2.8.6",
+    "dotenv": "^17.2.4",
+    "express": "^5.2.1",
+    "express-validator": "^7.3.1",
     "mongoose": "^9.1.6"
   }
 }