Feat/suggested questions

[Dakuan]

Summary by cubic

Add conversation starters (suggested questions) to Chat Apps to display preset prompts. Defaults to an empty list and persists via the Chat Apps API.

• New Features
  • Added ChatConversationStarter type and conversationStarters field to ChatApp.
  • Applied default [] when conversation starters are missing.
  • API accepts and stores conversationStarters via PUT /api/chatapps/:id; tests cover defaults and persistence.

^{Written for commit beb6da0. Summary will update on new commits.}