fix(frontend): pin the question as a stable first line during processing

The central column was top-anchored with no fixed header, so the user's
question was never shown while the model worked and the activity/gate
content drifted upward. Render the active session's question as a sticky,
always-present first row of the central area so it stays evident and
anchored at the top of the form.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/src/shell/AppShell.tsx

@@ -454,6 +454,14 @@ export function AppShell() {
           <div className="mx-auto flex max-w-4xl flex-col gap-6">
             {sessionViewOpen ? (
               <>
+                {activeSession?.question && (
+                  <header className="sticky top-0 z-10 -mx-6 -mt-8 border-b border-border/60 bg-background/95 px-6 pb-3 pt-8 backdrop-blur supports-[backdrop-filter]:bg-background/80">
+                    <p className="thot-label mb-0.5 text-muted-foreground">Domanda</p>
+                    <h2 className="font-heading text-[0.95rem] font-semibold leading-snug text-foreground break-words">
+                      {activeSession.question}
+                    </h2>
+                  </header>
+                )}
                 <CentralStatus working={working} />
                 {activeSessionId && <WidgetHost sessionId={activeSessionId} />}
                 {finalized && !agentActive && (