feat: two-step staging upload + multi-page PDF person inheritance

- Add stage/process-staged/remove-staged endpoints for batch upload workflow
- Add staging gallery UI with thumbnail previews and per-image removal
- Inherit person info & doc fields from page 1 for multi-page PDFs
- Auto-link page 2+ to same person on confirmation
- Show info banner on review page for multi-page documents
- Exclude staged docs from stats counters

templates/review.html

@@ -54,6 +54,18 @@
   <div class="form-panel">
     <form id="reviewForm">
 
+      {% if doc.get('pdf_group_id') and (doc.get('page_number') or 0) > 1 %}
+      <div class="info-banner page-group-banner">
+        <svg width="18" height="18" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round"><circle cx="12" cy="12" r="10"/><line x1="12" y1="16" x2="12" y2="12"/><line x1="12" y1="8" x2="12.01" y2="8"/></svg>
+        هذه الصفحة {{ doc.page_number }} من مستند متعدد الصفحات.
+        {% if doc.get('inherited_from_page1') %}
+        بيانات الشخص مستوردة تلقائياً من الصفحة الأولى.
+        {% else %}
+        يرجى التأكد من بيانات الشخص يدوياً.
+        {% endif %}
+      </div>
+      {% endif %}
+
       <!-- Person Info -->
       <section class="form-section">
         <h3>بيانات الشخص</h3>