feat: Unterordner-Navigation in Ordner-Freigaben

Geteilte Ordner koennen jetzt komplett durchnavigiert werden:

- Klick auf einen Unterordner oeffnet dessen Inhalt
- Breadcrumb-Navigation: Root > Unterordner > Unter-Unterordner
  mit Klick zurueck auf jede Ebene
- Ordner-Zeilen haben Hover-Effekt und Cursor-Pointer

Backend:
- GET /share/<token>/files?parent_id=X - Unterordner auflisten
- Sicherheitspruefung: parent_id muss innerhalb des geteilten
  Ordners liegen (_is_inside_shared_folder traversiert den Baum)
- Breadcrumb wird serverseitig berechnet
- Download + Delete erlauben jetzt Dateien in jeder Tiefe
  (nicht nur direkte Kinder)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/src/views/ShareView.vue

@@ -38,8 +38,16 @@
 
           <!-- Folder: file listing (read + write) -->
           <div v-if="fileInfo.is_folder && fileInfo.permission !== 'upload_only'" class="folder-content">
+            <div class="folder-breadcrumb">
+              <a class="crumb" @click="navigateToRoot">{{ fileInfo.name }}</a>
+              <template v-for="item in folderBreadcrumb" :key="item.id">
+                <i class="pi pi-angle-right crumb-sep"></i>
+                <a class="crumb" @click="navigateToFolder(item.id)">{{ item.name }}</a>
+              </template>
+            </div>
+
             <div class="folder-toolbar">
-              <span class="folder-count">{{ folderFiles.length }} Dateien</span>
+              <span class="folder-count">{{ folderFiles.length }} Eintraege</span>
               <Button v-if="fileInfo.upload_allowed" icon="pi pi-upload" label="Hochladen" size="small" @click="$refs.uploadInput.click()" />
             </div>
 
@@ -48,7 +56,8 @@
             </div>
 
             <div v-else class="file-list">
-              <div v-for="f in folderFiles" :key="f.id" class="file-item">
+              <div v-for="f in folderFiles" :key="f.id" class="file-item"
+                   :class="{ clickable: f.is_folder }" @click="f.is_folder && navigateToFolder(f.id)">
                 <div class="file-info">
                   <i :class="f.is_folder ? 'pi pi-folder' : 'pi pi-file'"></i>
                   <div class="file-details">
@@ -58,9 +67,9 @@
                 </div>
                 <div class="file-actions">
                   <Button v-if="!f.is_folder" icon="pi pi-download" text size="small"
-                          @click="downloadFolderFile(f)" />
+                          @click.stop="downloadFolderFile(f)" />
                   <Button v-if="fileInfo.permission === 'write'" icon="pi pi-trash" text size="small"
-                          severity="danger" @click="deleteFolderFile(f)" />
+                          severity="danger" @click.stop="deleteFolderFile(f)" />
                 </div>
               </div>
               <div v-if="!folderFiles.length" class="empty-folder">
@@ -122,6 +131,8 @@ const authError = ref('')
 const verifying = ref(false)
 
 const folderFiles = ref([])
+const folderBreadcrumb = ref([])
+const currentParentId = ref(null)
 const loadingFiles = ref(false)
 
 const isDragging = ref(false)
@@ -179,18 +190,31 @@ async function verifyPassword() {
   }
 }
 
-async function loadFolderFiles() {
+async function loadFolderFiles(parentId = null) {
   loadingFiles.value = true
   try {
-    const res = await axios.get(`/api/share/${token}/files`, { headers: getAuthHeaders() })
-    folderFiles.value = res.data
+    const params = {}
+    if (parentId) params.parent_id = parentId
+    const res = await axios.get(`/api/share/${token}/files`, { params, headers: getAuthHeaders() })
+    folderFiles.value = res.data.files
+    folderBreadcrumb.value = res.data.breadcrumb || []
+    currentParentId.value = res.data.current_parent_id
   } catch {
     folderFiles.value = []
+    folderBreadcrumb.value = []
   } finally {
     loadingFiles.value = false
   }
 }
 
+function navigateToFolder(folderId) {
+  loadFolderFiles(folderId)
+}
+
+function navigateToRoot() {
+  loadFolderFiles(null)
+}
+
 function downloadFile() {
   let url = `/api/share/${token}/download`
   if (fileInfo.value?.has_password && password.value) {
@@ -287,6 +311,13 @@ onMounted(loadInfo)
 
 /* Folder content */
 .folder-content { margin-bottom: 1.5rem; }
+.folder-breadcrumb {
+  display: flex; align-items: center; gap: 0.25rem; margin-bottom: 0.75rem;
+  font-size: 0.9rem;
+}
+.crumb { cursor: pointer; color: var(--p-primary-color); font-weight: 500; }
+.crumb:hover { text-decoration: underline; }
+.crumb-sep { font-size: 0.7rem; color: var(--p-surface-400); }
 .folder-toolbar {
   display: flex; align-items: center; justify-content: space-between;
   margin-bottom: 0.75rem; padding-bottom: 0.5rem; border-bottom: 1px solid var(--p-surface-200);
@@ -297,6 +328,8 @@ onMounted(loadInfo)
   display: flex; align-items: center; justify-content: space-between;
   padding: 0.5rem 0; border-bottom: 1px solid var(--p-surface-100);
 }
+.file-item.clickable { cursor: pointer; }
+.file-item.clickable:hover { background: var(--p-surface-50); }
 .file-info { display: flex; align-items: center; gap: 0.5rem; flex: 1; min-width: 0; }
 .file-info i { font-size: 1.1rem; color: var(--p-surface-500); flex-shrink: 0; }
 .file-details { display: flex; flex-direction: column; min-width: 0; }