feat: Add Swagger API documentation

This commit introduces Swagger API documentation for all endpoints in the
application.

- Installs  and .
- Configures Swagger in  to generate and serve API documentation
  at .
- Adds JSDoc-style Swagger annotations to all routes in  and
  the  directory (, , ,
  , , ).
- Defines a cookie-based security scheme for authenticated routes.

This allows for interactive API documentation and testing via the
endpoint.

package.json

@@ -30,6 +30,8 @@
     "posthog-node": "^4.4.1",
     "socket.io": "^4.6.1",
     "stripe": "^8.178.0",
+    "swagger-jsdoc": "^6.2.8",
+    "swagger-ui-express": "^5.0.1",
     "web-push": "^3.4.5"
   },
   "devDependencies": {