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>

frontend/src/components/ui/MarkdownContent.tsx

@@ -79,9 +79,9 @@ export function MarkdownContent({ content, className }: MarkdownContentProps) {
         ),
         // Style horizontal rules
         hr: () => <hr className="my-4 border-border" />,
-        // Style blockquotes
+        // Style blockquotes — used for AI questions/action items that need to stand out
         blockquote: ({ children }) => (
-          <blockquote className="mb-3 border-l-4 border-border pl-4 italic text-muted-foreground last:mb-0">
+          <blockquote className="mb-3 rounded-lg border border-accent/20 bg-accent-dim/50 px-4 py-3 not-italic text-heading last:mb-0">
             {children}
           </blockquote>
         ),