Register FCM device token for push notifications

Request

• Base URL
  https://api.insighto.ai (the document declares no server; this is the origin it was published from)
• Auth
  • API key in query parameter api_key
  • or HTTP bearer
• TypeScript
  https://skmtc.dev/insighto/apis/ragify/docs/api/v1/users/me/device_token/post.ts

  A function with typed inputs. Its response is checked against the schema.