Improve admin snapshot list/grid views with better UX

- Add prominent view mode switcher with List/Grid toggle buttons
- Improve filter sidebar CSS with modern styling, rounded corners
- Add live progress bar for in-progress snapshots showing hooks status
- Show plugin icons only when output directory has content
- Display archive result output_size sum from new field
- Show hooks succeeded/total count in size column
- Add get_progress_stats() method to Snapshot model
- Add CSS for progress spinner and status badges
- Update grid view template with progress indicator for archiving cards
- Add tests for admin views, search, and progress stats

archivebox/templates/admin/snapshots_grid.html

@@ -126,6 +126,21 @@
   .cards .card .card-info .timestamp {
       font-weight: 600;
   }
+  .cards .card .card-progress {
+      display: flex;
+      align-items: center;
+      gap: 6px;
+      padding: 4px 0;
+  }
+  .cards .card .card-progress .progress-text {
+      font-size: 11px;
+      color: #3b82f6;
+      font-weight: 500;
+  }
+  .cards .card.archiving {
+      border-color: #3b82f6;
+      box-shadow: 0 0 0 2px rgba(59, 130, 246, 0.2);
+  }
   .cards .card .card-footer code {
       display: inline-block;
       width: 100%;
@@ -145,14 +160,21 @@
 {% block content %}
   <section class="cards">
     {% for obj in results %}
-      <div class="card">
+      <div class="card{% if obj.status == 'started' %} archiving{% endif %}">
           <div class="card-info">
             <a href="{% url 'admin:core_snapshot_change' obj.pk %}">
               <span class="timestamp">{{obj.bookmarked_at}}</span>
             </a>
-            <div style="padding: 4px 0;">
-              {{ obj.icons|safe }}
-            </div>
+            {% if obj.status == 'started' %}
+              <div class="card-progress">
+                <span class="snapshot-progress-spinner"></span>
+                <span class="progress-text">Archiving...</span>
+              </div>
+            {% else %}
+              <div style="padding: 4px 0;">
+                {{ obj.icons|safe }}
+              </div>
+            {% endif %}
             <label>
               <span>🗄&nbsp; {{ obj.archive_size | file_size }}</span>
               <input type="checkbox" name="_selected_action" value="{{obj.pk}}"/>