ProfileCard: validate nickname, occupation, link, and image

[mikanIchinose]

Background

Previously, only a nickname was a required field, but the specifications have been changed so that occupation, link, and image are now also mandatory.

Spec

• data: change all properties of ProfileCard to non-null
  • https://github.com/DroidKaigi/conference-app-2024/blob/e877e6d649365d871a41911b64ba892583cfca50/core/model/src/commonMain/kotlin/io/github/droidkaigi/confsched/model/ProfileCard.kt#L8-L14
  • https://github.com/DroidKaigi/conference-app-2024/blob/e877e6d649365d871a41911b64ba892583cfca50/core/data/src/commonMain/kotlin/io/github/droidkaigi/confsched/data/profilecard/ProfileCardJson.kt#L8-L14
• ui: change field required
  • occupation
  • link
  • image
• ui: validate form
  • nickname
  • occupation
  • link
  • image

error state

[Corvus400]

I've finished other tasks, so I'd like to start working on this one. 🙋

[mikanIchinose]

Thank you. Assigned.