refactor(10-12): migrate folder/document/upload/sharing SVGs to AppIcon

- FolderRow.vue: folder icon + dots menu button (fill-based → stroke AppIcon)
- FolderTreeItem.vue: folder icon in #icon slot
- FolderDeleteModal.vue: warning icon
- DocumentCard.vue: document, folderMove, share action icons
- DocumentPreviewModal.vue: x close button (spinner SVG kept)
- ShareModal.vue: x close button
- DropZone.vue: upload icon
- UploadProgress.vue: exclamationCircle (error) + checkCircle (done) icons; spinner kept

frontend/src/components/documents/DocumentCard.vue

@@ -6,10 +6,7 @@
     <div class="flex items-start gap-3">
       <!-- Icon -->
       <div class="w-9 h-9 rounded-lg bg-indigo-50 flex items-center justify-center shrink-0 mt-0.5">
-        <svg class="w-5 h-5 text-indigo-500" fill="none" stroke="currentColor" viewBox="0 0 24 24">
-          <path stroke-linecap="round" stroke-linejoin="round" stroke-width="2"
-            d="M9 12h6m-6 4h6m2 5H7a2 2 0 01-2-2V5a2 2 0 012-2h5.586a1 1 0 01.707.293l5.414 5.414a1 1 0 01.293.707V19a2 2 0 01-2 2z" />
-        </svg>
+        <AppIcon name="document" class="w-5 h-5 text-indigo-500" />
       </div>
 
       <div class="flex-1 min-w-0">
@@ -67,10 +64,7 @@
             aria-label="Move to folder"
             class="min-h-[44px] min-w-[44px] flex items-center justify-center p-2 rounded-md text-gray-400 hover:text-indigo-600 hover:bg-indigo-50 transition-colors"
           >
-            <svg class="w-4 h-4" fill="none" stroke="currentColor" viewBox="0 0 24 24">
-              <path stroke-linecap="round" stroke-linejoin="round" stroke-width="2"
-                d="M3 7a2 2 0 012-2h4l2 2h8a2 2 0 012 2v8a2 2 0 01-2 2H5a2 2 0 01-2-2V7z" />
-            </svg>
+            <AppIcon name="folderMove" class="w-4 h-4" />
           </button>
         </div>
         <!-- Share -->
@@ -79,10 +73,7 @@
           aria-label="Share document"
           class="min-h-[44px] min-w-[44px] flex items-center justify-center p-2 rounded-md text-gray-400 hover:text-indigo-600 hover:bg-indigo-50 transition-colors"
         >
-          <svg class="w-4 h-4" fill="none" stroke="currentColor" viewBox="0 0 24 24">
-            <path stroke-linecap="round" stroke-linejoin="round" stroke-width="2"
-              d="M8.684 13.342C8.886 12.938 9 12.482 9 12c0-.482-.114-.938-.316-1.342m0 2.684a3 3 0 110-2.684m0 2.684l6.632 3.316m-6.632-6l6.632-3.316m0 0a3 3 0 105.367-2.684 3 3 0 00-5.367 2.684zm0 9.316a3 3 0 105.368 2.684 3 3 0 00-5.368-2.684z" />
-          </svg>
+          <AppIcon name="share" class="w-4 h-4" />
         </button>
       </div>
     </div>
@@ -123,6 +114,7 @@
 
 <script setup>
 import { ref, computed, onMounted, onUnmounted } from 'vue'
+import AppIcon from '../ui/AppIcon.vue'
 import { useTopicsStore } from '../../stores/topics.js'
 import { useFoldersStore } from '../../stores/folders.js'
 import { moveDocument, classifyDocument } from '../../api/client.js'