fix(flowpilot): render markdown in context messages + fix action bar height chain

Two issues:
1. AI context messages (teal bubble) rendered raw markdown (**bold** etc.)
   instead of parsed markdown — switched from <p> to <MarkdownContent>
2. Action bar still hidden — added h-0 to flex-1 wrapper to force explicit
   height allocation so h-full on FlowPilotSession resolves correctly

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/src/components/flowpilot/FlowPilotStepCard.tsx

@@ -116,7 +116,7 @@ export function FlowPilotStepCard({ step, isCurrentStep, isProcessing, sessionId
       {/* Context message */}
       {step.context_message && (
         <div className="mb-3 rounded-lg bg-primary/5 px-3 py-2 border border-primary/10">
-          <p className="text-xs text-muted-foreground">{step.context_message}</p>
+          <MarkdownContent content={step.context_message} className="text-xs text-muted-foreground" />
         </div>
       )}