fix(chore): keep start/dev scripts without .env, add separate billing scripts

start/dev remain unchanged so the app works without Stripe.
start:billing/dev:billing load .env for Stripe testing.

Author: PierreBrisorgueil

package.json

@@ -23,8 +23,10 @@
     "node": ">=22.0.0"
   },
   "scripts": {
-    "start": "node --env-file-if-exists=.env server.js",
-    "dev": "node --env-file-if-exists=.env --watch server.js",
+    "start": "node server.js",
+    "start:billing": "node --env-file-if-exists=.env server.js",
+    "dev": "node --watch server.js",
+    "dev:billing": "node --env-file-if-exists=.env --watch server.js",
     "debug": "nodemon --inspect server.js",
     "prod": "cross-env NODE_ENV=production node server.js --name=node",
     "test": "cross-env NODE_ENV=test NODE_OPTIONS=--experimental-vm-modules jest --runInBand --testPathPatterns='unit'",