fix(ui): status page — null safety, preview visibility, error handling

templates/status.html

@@ -29,7 +29,7 @@
     {% endif %}
   </div>
 
-  <div class="live-preview-section card" id="live-preview-section" style="display: {{ 'block' if job.status.name in ['RUNNING', 'PENDING'] else 'none' }}">
+  <div class="live-preview-section card" id="live-preview-section" style="display: block">
     <h3 class="section-title">Live Preview</h3>
     <div class="live-preview-wrap">
       <img id="live-preview-img" class="live-preview-img" alt="Annotated frame from processing" />