feat: Share-Links mit Berechtigungen (Lesen / Lesen+Schreiben)

Share-Links haben jetzt ein permission-Feld (read/write):

- read (Standard): Nur Download erlaubt, kein Upload, kein Aendern
- write: Download + Upload in Ordner erlaubt

Backend-Absicherung:
- POST /share/<token>/upload prueft permission == 'write', gibt 403
  bei read-only Links zurueck
- GET /share/<token>/info gibt permission + upload_allowed zurueck
- ShareLink-Model hat neues permission-Feld (default: 'read')

Frontend Share-Dialog:
- Dropdown "Berechtigung" beim Erstellen von Links
  (Nur Lesen / Lesen+Hochladen)
- Bestehende Links zeigen Berechtigungslevel an

Frontend ShareView:
- Upload-Zone nur sichtbar wenn upload_allowed == true
- Bei read-only Links: kein Drag & Drop, kein Upload-Button

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

frontend/src/views/FilesView.vue

@@ -162,6 +162,10 @@
         <div class="share-section">
           <h5>Freigabe-Link erstellen</h5>
           <div class="share-form">
+            <div class="field">
+              <label>Berechtigung</label>
+              <Select v-model="shareLinkPermission" :options="linkPermOptions" optionLabel="label" optionValue="value" fluid />
+            </div>
             <div class="field">
               <label>Passwort (optional)</label>
               <Password v-model="sharePassword" :feedback="false" toggle-mask fluid />
@@ -180,7 +184,8 @@
             <div class="link-info">
               <code>{{ currentOrigin }}/share/{{ link.token }}</code>
               <small>
-                {{ link.download_count }} Downloads
+                {{ link.permission === 'write' ? 'Lesen+Schreiben' : 'Nur Lesen' }}
+                | {{ link.download_count }} Downloads
                 <template v-if="link.expires_at"> | Bis {{ formatDate(link.expires_at) }}</template>
                 <template v-if="link.has_password"> | Passwortgeschuetzt</template>
               </small>
@@ -250,6 +255,8 @@ const selectedShareUser = ref(null)
 const shareUserPermission = ref('read')
 const userSearchResults = ref([])
 const userPermOptions = [{ label: 'Lesen', value: 'read' }, { label: 'Schreiben', value: 'write' }, { label: 'Admin', value: 'admin' }]
+const linkPermOptions = [{ label: 'Nur Lesen (Download)', value: 'read' }, { label: 'Lesen + Hochladen (nur Ordner)', value: 'write' }]
+const shareLinkPermission = ref('read')
 const currentOrigin = window.location.origin
 const shareLoading = ref(false)
 const showDeleteConfirm = ref(false)
@@ -580,13 +587,14 @@ async function createShare() {
   if (!shareFile.value) return
   shareLoading.value = true
   try {
-    const opts = {}
+    const opts = { permission: shareLinkPermission.value }
     if (sharePassword.value) opts.password = sharePassword.value
     if (shareExpiry.value) opts.expires_at = shareExpiry.value
     await filesStore.createShareLink(shareFile.value.id, opts)
     shareLinks.value = await filesStore.getShareLinks(shareFile.value.id)
     sharePassword.value = ''
     shareExpiry.value = ''
+    shareLinkPermission.value = 'read'
     toast.add({ severity: 'success', summary: 'Link erstellt', life: 3000 })
   } catch (err) {
     toast.add({ severity: 'error', summary: 'Fehler', detail: err.response?.data?.error, life: 5000 })