Sécurisation de l'API et refonte des tests backend

- helmet et express-rate-limit sur les routes d'authentification
- CORS restreint aux origines de FRONTEND_URL
- CSP désactivée uniquement sur /api-docs pour Swagger UI
- ajout du test de tirage et simplification du test e2e
- suppression de tests/setup.js devenu inutile

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

backend/package-lock.json

@@ -13,6 +13,8 @@
         "bcrypt": "^6.0.0",
         "cors": "^2.8.6",
         "express": "^5.2.1",
+        "express-rate-limit": "^8.6.1",
+        "helmet": "^8.3.0",
         "jsonwebtoken": "^9.0.3",
         "nodemailer": "^9.0.3",
         "prisma": "^6.19.3",
@@ -605,9 +607,9 @@
       "license": "MIT"
     },
     "node_modules/@emnapi/wasi-threads": {
-      "version": "1.2.2",
-      "resolved": "https://registry.npmjs.org/@emnapi/wasi-threads/-/wasi-threads-1.2.2.tgz",
-      "integrity": "sha512-c95qOXkHdydNKhscBTebqEC1CVAZpyqOfVfBzQ1qgzyl3gfeldUjIggDbIZgDKsHLgnsM+igH7TJ/eAasaVuMA==",
+      "version": "1.2.3",
+      "resolved": "https://registry.npmjs.org/@emnapi/wasi-threads/-/wasi-threads-1.2.3.tgz",
+      "integrity": "sha512-ELEBe8PsLvvJ6QMr0zLt8ffvOHW/dc1m3CEzNMg7aJUv3bMaoDtw2TXyDAwkYBuroxxuHEwhRTLJSe5sya547g==",
       "dev": true,
       "license": "MIT",
       "optional": true,
@@ -3187,6 +3189,25 @@
         "url": "https://opencollective.com/express"
       }
     },
+    "node_modules/express-rate-limit": {
+      "version": "8.6.1",
+      "resolved": "https://registry.npmjs.org/express-rate-limit/-/express-rate-limit-8.6.1.tgz",
+      "integrity": "sha512-0D493aP61w0TJ2A0wy27riRsO7FMQ7FK+KUHOKCSfPvYo0R55aiC6emCVgFUeShH0fq0ICPVzNcgoS+BsbXQCA==",
+      "license": "MIT",
+      "dependencies": {
+        "debug": "^4.4.3",
+        "ip-address": "^10.2.0"
+      },
+      "engines": {
+        "node": ">= 16"
+      },
+      "funding": {
+        "url": "https://github.com/sponsors/express-rate-limit"
+      },
+      "peerDependencies": {
+        "express": ">= 4.11"
+      }
+    },
     "node_modules/exsolve": {
       "version": "1.0.8",
       "resolved": "https://registry.npmjs.org/exsolve/-/exsolve-1.0.8.tgz",
@@ -3635,6 +3656,18 @@
         "node": ">= 0.4"
       }
     },
+    "node_modules/helmet": {
+      "version": "8.3.0",
+      "resolved": "https://registry.npmjs.org/helmet/-/helmet-8.3.0.tgz",
+      "integrity": "sha512-Qgpiaws3Sm30Av8Eah6sjMCZZwjlBu+E68rhpCWBshY1lb09HtLwj5GviX0OyQIn+ulUS0iX0AxN5n3tLZzz1w==",
+      "license": "MIT",
+      "engines": {
+        "node": ">=18.0.0"
+      },
+      "funding": {
+        "url": "https://github.com/sponsors/EvanHahn"
+      }
+    },
     "node_modules/html-escaper": {
       "version": "2.0.2",
       "resolved": "https://registry.npmjs.org/html-escaper/-/html-escaper-2.0.2.tgz",
@@ -3743,6 +3776,15 @@
       "integrity": "sha512-k/vGaX4/Yla3WzyMCvTQOXYeIHvqOKtnqBduzTHpzpQZzAskKMhZ2K+EnBiSM9zGSoIFeMpXKxa4dYeZIQqewQ==",
       "license": "ISC"
     },
+    "node_modules/ip-address": {
+      "version": "10.4.0",
+      "resolved": "https://registry.npmjs.org/ip-address/-/ip-address-10.4.0.tgz",
+      "integrity": "sha512-oSK96Grm3aP6OrS263xVxbNDGVL7rzBtYdpGqlDG8iQdoenDoTs/nkki+DflYbAEE8Xl6o5YxhxlrKvI3nqKXQ==",
+      "license": "MIT",
+      "engines": {
+        "node": ">= 12"
+      }
+    },
     "node_modules/ipaddr.js": {
       "version": "1.9.1",
       "resolved": "https://registry.npmjs.org/ipaddr.js/-/ipaddr.js-1.9.1.tgz",