feat: AI marker system prompt fixes, TaskLane activation, and FlowPilot updates

- Fix system prompt to ensure [QUESTIONS]/[ACTIONS] markers in AI responses
- Add format reminder injection to user messages for marker compliance
- Wire TaskLane activation in prefill and resume paths
- Add ActionCardGroup component for structured question/action rendering
- Update FlowPilot session and step card components
- Update ai-session schemas and types for marker data

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/app/api/endpoints/ai_sessions.py

@@ -287,7 +287,7 @@ async def send_chat_message(
         images = await fetch_upload_images(data.upload_ids, account_id, db) or None
 
     try:
-        ai_content, suggested_flows, session = await unified_chat_service.send_chat_message(
+        ai_content, suggested_flows, session, fork_metadata, actions_data, questions_data = await unified_chat_service.send_chat_message(
             session_id=session_id,
             user_id=user_id,
             account_id=account_id,
@@ -329,6 +329,9 @@ async def send_chat_message(
     return ChatMessageResponse(
         content=ai_content,
         suggested_flows=suggested_flows,
+        fork=fork_metadata,
+        actions=actions_data,
+        questions=questions_data,
     )