feat: implement backend episode management and progress tracking controllers and routes

backend/package.json

@@ -23,7 +23,10 @@
     "cors": "^2.8.5",
     "zod": "^3.22.4",
     "rss-parser": "^3.12.0",
-    "axios": "^1.5.0"
+    "axios": "^1.5.0",
+    "node-cron": "^3.0.3",
+    "helmet": "^7.1.0",
+    "express-rate-limit": "^7.1.5"
   },
   "devDependencies": {
     "@types/express": "^4.17.20",