fix: Client-Upload akzeptiert SECRET_KEY oder JWT_SECRET_KEY + Download in Settings

Upload-Auth:
- Akzeptiert jetzt sowohl SECRET_KEY als auch JWT_SECRET_KEY
  (BUILD_UPLOAD_TOKEN in Entwicklungs-.env kann einer von beiden sein)

Settings-View:
- Zeigt verfuegbare Desktop/Mobile Clients zum Download an
  (nur wenn mindestens ein Client vorhanden)
- Pro Client: Name, Dateiname, Download-Button

.env.example:
- Klarere Kommentare: "SECRET_KEY oder JWT_SECRET_KEY des Zielservers"

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

frontend/src/views/SettingsView.vue

@@ -45,6 +45,24 @@
       </form>
     </div>
 
+    <!-- Client Downloads -->
+    <div v-if="availableClients.length" class="settings-section">
+      <h3>Desktop & Mobile Clients</h3>
+      <div class="client-list">
+        <div v-for="client in availableClients" :key="client.platform" class="client-item">
+          <div class="client-info">
+            <i :class="'pi ' + (client.platform === 'linux' || client.platform === 'windows' || client.platform === 'mac' ? 'pi-desktop' : 'pi-mobile')"></i>
+            <div>
+              <strong>{{ client.name }}</strong>
+              <span class="client-meta">{{ client.filename }}</span>
+            </div>
+          </div>
+          <Button icon="pi pi-download" :label="'Download'" size="small" outlined
+                  @click="downloadClient(client)" />
+        </div>
+      </div>
+    </div>
+
     <!-- Email Accounts -->
     <div class="settings-section">
       <div class="section-header">
@@ -167,6 +185,13 @@ import InputSwitch from 'primevue/inputswitch'
 const auth = useAuthStore()
 const toast = useToast()
 
+// Client downloads
+const availableClients = ref([])
+
+function downloadClient(client) {
+  window.location.href = `/api/clients/${client.platform}/download`
+}
+
 // --- Password change ---
 const currentPassword = ref('')
 const newPassword = ref('')
@@ -307,7 +332,13 @@ async function doDeleteAccount() {
   }
 }
 
-onMounted(loadAccounts)
+onMounted(async () => {
+  loadAccounts()
+  try {
+    const res = await apiClient.get('/clients')
+    availableClients.value = res.data.clients
+  } catch { availableClients.value = [] }
+})
 </script>
 
 <style scoped>
@@ -346,4 +377,12 @@ onMounted(loadAccounts)
 .field label { display: block; margin-bottom: 0.5rem; font-weight: 500; font-size: 0.875rem; }
 .field-row { display: flex; gap: 0.75rem; align-items: flex-end; }
 .flex-grow { flex: 1; }
+.client-list { display: flex; flex-direction: column; gap: 0.5rem; }
+.client-item {
+  display: flex; align-items: center; justify-content: space-between;
+  padding: 0.75rem; border: 1px solid var(--p-surface-200); border-radius: 8px;
+}
+.client-info { display: flex; align-items: center; gap: 0.75rem; }
+.client-info i { font-size: 1.25rem; color: var(--p-primary-color); }
+.client-meta { display: block; font-size: 0.8rem; color: var(--p-text-muted-color); }
 </style>