Monitor e quota registrata mostrano NaN invece di andare in errore (Refs #118)

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_019A9CSrh9rfM5WwqKtg8BSE

src/frontend/flask_app/templates/measure/task_execute.html

@@ -472,7 +472,8 @@
             <path stroke-linecap="round" stroke-linejoin="round" d="M5 13l4 4L19 7"/>
           </svg>
           <span>{{ _('Registrata') }}:</span>
-          <span class="font-mono font-bold" x-text="getMeasuredValue(currentSubtask?.id)?.toFixed(3) || '—'"></span>
+          {# #118: quota registrata senza valore (visione, NaN) #}
+          <span class="font-mono font-bold" x-text="getMeasuredValue(currentSubtask?.id)?.toFixed(3) ?? 'NaN'"></span>
           <span x-text="currentSubtask?.unit || 'mm'"></span>
         </div>
       </div>