feat: Bestehende Benutzerfreigaben per Stift-Button bearbeiten

Neben der Muelltonne jetzt ein Stift-Icon im Share-Dialog:
Klick macht die Zeile zur Inline-Edit-Zeile mit Permission-
Dropdown + Weiterteilen-Checkbox + Speichern/Abbrechen-Buttons.
Speichern ruft POST /permissions mit user_id auf - Backend
erkennt die bestehende Freigabe und aktualisiert sie, statt
loeschen + neu anlegen zu muessen.

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

frontend/src/views/FilesView.vue

@@ -187,13 +187,26 @@
             </div>
           </div>
           <div v-if="filePermissions.length" class="existing-shares">
-            <div v-for="perm in filePermissions" :key="perm.id" class="share-perm-item">
+            <template v-for="perm in filePermissions" :key="perm.id">
-              <i class="pi pi-user"></i>
+              <div v-if="editingPermId !== perm.id" class="share-perm-item">
-              <span>{{ perm.username }}</span>
+                <i class="pi pi-user"></i>
-              <Tag :value="permLabel(perm.permission)" size="small" />
+                <span>{{ perm.username }}</span>
-              <Tag v-if="perm.can_reshare" value="darf weiterteilen" severity="info" size="small" />
+                <Tag :value="permLabel(perm.permission)" size="small" />
-              <Button icon="pi pi-trash" text size="small" severity="danger" @click="removeUserShare(perm.id)" />
+                <Tag v-if="perm.can_reshare" value="darf weiterteilen" severity="info" size="small" />
-            </div>
+                <Button icon="pi pi-pencil" text size="small" @click="startEditPerm(perm)" title="Bearbeiten" />
+                <Button icon="pi pi-trash" text size="small" severity="danger" @click="removeUserShare(perm.id)" title="Entfernen" />
+              </div>
+              <div v-else class="share-perm-item editing">
+                <i class="pi pi-user"></i>
+                <span>{{ perm.username }}</span>
+                <Select v-model="editPermValue" :options="availableUserPermOptions" optionLabel="label" optionValue="value" />
+                <label class="reshare-check">
+                  <input type="checkbox" v-model="editPermReshare" /> darf weiterteilen
+                </label>
+                <Button icon="pi pi-check" text size="small" severity="success" @click="saveEditPerm(perm)" title="Speichern" />
+                <Button icon="pi pi-times" text size="small" @click="cancelEditPerm" title="Abbrechen" />
+              </div>
+            </template>
           </div>
         </div>
 
@@ -295,6 +308,9 @@ const shareUserQuery = ref('')
 const selectedShareUser = ref(null)
 const shareUserPermission = ref('read')
 const shareUserReshare = ref(false)
+const editingPermId = ref(null)
+const editPermValue = ref('read')
+const editPermReshare = ref(false)
 const userSearchResults = ref([])
 const userPermOptions = [{ label: 'Lesen', value: 'read' }, { label: 'Schreiben', value: 'write' }, { label: 'Admin', value: 'admin' }]
 const linkPermOptions = [
@@ -684,6 +700,34 @@ async function removeUserShare(permId) {
   }
 }
 
+function startEditPerm(perm) {
+  editingPermId.value = perm.id
+  editPermValue.value = perm.permission
+  editPermReshare.value = !!perm.can_reshare
+}
+
+function cancelEditPerm() {
+  editingPermId.value = null
+}
+
+async function saveEditPerm(perm) {
+  if (!shareFile.value) return
+  try {
+    await apiClient.post(`/files/${shareFile.value.id}/permissions`, {
+      user_id: perm.user_id,
+      permission: editPermValue.value,
+      can_reshare: editPermReshare.value,
+    })
+    const res = await apiClient.get(`/files/${shareFile.value.id}/permissions`)
+    filePermissions.value = res.data
+    editingPermId.value = null
+    toast.add({ severity: 'success', summary: 'Berechtigung aktualisiert', life: 2500 })
+    await filesStore.loadFiles(currentParentId())
+  } catch (err) {
+    toast.add({ severity: 'error', summary: 'Fehler', detail: err.response?.data?.error || err.message, life: 5000 })
+  }
+}
+
 async function createShare() {
   console.log('createShare called, shareFile:', shareFile.value?.id, 'permission:', shareLinkPermission.value)
   if (!shareFile.value) {
@@ -886,7 +930,8 @@ onUnmounted(() => {
 .user-result { padding: 0.5rem 0.75rem; cursor: pointer; display: flex; align-items: center; gap: 0.5rem; font-size: 0.875rem; }
 .user-result:hover, .user-result.selected { background: var(--p-primary-50); }
 .existing-shares { margin-top: 0.5rem; }
-.share-perm-item { display: flex; align-items: center; gap: 0.5rem; padding: 0.375rem 0; font-size: 0.875rem; }
+.share-perm-item { display: flex; align-items: center; gap: 0.5rem; padding: 0.375rem 0; font-size: 0.875rem; flex-wrap: wrap; }
+.share-perm-item.editing { background: var(--p-surface-50); padding: 0.5rem; border-radius: 4px; }
 .share-link-item {
   display: flex; justify-content: space-between; align-items: center;
   padding: 0.5rem 0; border-bottom: 1px solid var(--p-surface-100);