feat: token refresh, video upload, playlist routes complets

- auth: cookie od_token 7j, refresh token od_refresh 30j, POST /api/auth/refresh, GET /api/auth/me/optional
- admin: POST /api/admin/videos/upload via multer (mp4/webm, 4Go max, UUID filename)
- playlist: PATCH /:id, DELETE /:id, POST /:id/videos, DELETE /:id/videos/:videoId
- env: UPLOADS_DIR documenté dans .env.example

backend/package.json

@@ -19,6 +19,7 @@
     "dotenv": "^16.4.5",
     "express": "^4.18.3",
     "jsonwebtoken": "^9.0.2",
+    "multer": "^2.1.1",
     "mysql2": "^3.9.3",
     "reflect-metadata": "^0.2.2",
     "typeorm": "^0.3.20"
@@ -29,6 +30,7 @@
     "@types/cors": "^2.8.17",
     "@types/express": "^4.17.21",
     "@types/jsonwebtoken": "^9.0.6",
+    "@types/multer": "^2.1.0",
     "@types/node": "^20.12.2",
     "ts-node": "^10.9.2",
     "ts-node-dev": "^2.0.0",