feat(ST-0vtnydpi): Chat & Timeline tab — userQuestion rendering + UserChatInput
- IdeaTimeline: merge user_question entries into timeline (MessageCircle icon,
pending/answered states); show UserChatInput below ol when planMd present
- UserChatInput: Textarea + submit button calling createUserQuestionAction,
router.refresh() on success, sonner toast for errors
- IdeaDetailLayout: rename tab label to 'Chat & Timeline'; pass userQuestions,
planMd, ideaId props to IdeaTimeline; export IdeaUserQuestionDto interface
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>