feat: Client-Download-System + Auto-Upload nach Build

Backend:
- GET /api/clients - Verfuegbare Clients auflisten (oeffentlich)
- GET /api/clients/<platform>/download - Client herunterladen (oeffentlich)
- POST /api/clients/<platform>/upload - Build hochladen (BUILD_UPLOAD_TOKEN)
- Alte Version wird automatisch bei neuem Upload ersetzt
- Plattformen: linux, windows, mac, android, ios

Frontend:
- /clients - Download-Seite mit Grid aller verfuegbaren Clients
- Login-Seite zeigt "Desktop & Mobile Clients herunterladen" Link
  wenn mindestens ein Client verfuegbar ist

build.sh:
- Nach jedem Build wird der Client automatisch auf CLOUD_URL
  hochgeladen (wenn CLOUD_URL + BUILD_UPLOAD_TOKEN in .env gesetzt)
- Bestes Format pro Plattform: AppImage > .deb > Binary (Linux),
  .msi > .exe (Windows), .dmg (Mac), .apk (Android), .ipa (iOS)

.env.example:
- CLOUD_URL: Oeffentliche URL der Cloud-Instanz
- BUILD_UPLOAD_TOKEN: Auth-Token fuer Build-Upload

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

frontend/src/views/ClientsView.vue

@@ -0,0 +1,100 @@
+<template>
+  <div class="clients-container">
+    <div class="clients-card">
+      <div class="clients-header">
+        <i class="pi pi-cloud" style="font-size: 2rem; color: var(--p-primary-color)"></i>
+        <h1>Mini-Cloud Clients</h1>
+        <p>Lade den Sync-Client fuer dein Geraet herunter</p>
+      </div>
+
+      <div v-if="loading" class="loading">
+        <i class="pi pi-spin pi-spinner"></i> Laden...
+      </div>
+
+      <div v-else-if="!clients.length" class="empty">
+        <p>Noch keine Clients verfuegbar.</p>
+      </div>
+
+      <div v-else class="clients-grid">
+        <div v-for="client in clients" :key="client.platform" class="client-card">
+          <div class="client-icon">
+            <i :class="'pi ' + platformIcon(client.platform)"></i>
+          </div>
+          <h3>{{ client.name }}</h3>
+          <p class="client-meta">{{ client.filename }} ({{ formatSize(client.size) }})</p>
+          <Button :label="'Download ' + client.name" icon="pi pi-download"
+                  @click="downloadClient(client)" fluid />
+        </div>
+      </div>
+
+      <div class="clients-footer">
+        <router-link to="/login">Zurueck zur Anmeldung</router-link>
+      </div>
+    </div>
+  </div>
+</template>
+
+<script setup>
+import { ref, onMounted } from 'vue'
+import axios from 'axios'
+import Button from 'primevue/button'
+
+const clients = ref([])
+const loading = ref(true)
+
+const platformIcons = {
+  linux: 'pi-desktop',
+  windows: 'pi-desktop',
+  mac: 'pi-desktop',
+  android: 'pi-mobile',
+  ios: 'pi-mobile',
+}
+
+function platformIcon(platform) {
+  return platformIcons[platform] || 'pi-download'
+}
+
+function formatSize(bytes) {
+  if (!bytes) return ''
+  const units = ['B', 'KB', 'MB', 'GB']
+  let i = 0; let size = bytes
+  while (size >= 1024 && i < units.length - 1) { size /= 1024; i++ }
+  return `${size.toFixed(i > 0 ? 1 : 0)} ${units[i]}`
+}
+
+function downloadClient(client) {
+  window.location.href = `/api/clients/${client.platform}/download`
+}
+
+onMounted(async () => {
+  try {
+    const res = await axios.get('/api/clients')
+    clients.value = res.data.clients
+  } catch { clients.value = [] }
+  loading.value = false
+})
+</script>
+
+<style scoped>
+.clients-container {
+  min-height: 100vh; display: flex; align-items: center; justify-content: center;
+  background: var(--p-surface-50); padding: 1rem;
+}
+.clients-card {
+  background: var(--p-surface-0); border-radius: 12px; padding: 2.5rem;
+  max-width: 700px; width: 100%; box-shadow: 0 2px 12px rgba(0,0,0,0.08);
+}
+.clients-header { text-align: center; margin-bottom: 2rem; }
+.clients-header h1 { font-size: 1.5rem; margin: 0.5rem 0 0.25rem; }
+.clients-header p { color: var(--p-text-muted-color); margin: 0; }
+.clients-grid { display: grid; grid-template-columns: repeat(auto-fill, minmax(200px, 1fr)); gap: 1rem; }
+.client-card {
+  border: 1px solid var(--p-surface-200); border-radius: 8px; padding: 1.25rem; text-align: center;
+}
+.client-icon { font-size: 2rem; color: var(--p-primary-color); margin-bottom: 0.5rem; }
+.client-card h3 { margin: 0 0 0.25rem; font-size: 1rem; }
+.client-meta { font-size: 0.8rem; color: var(--p-text-muted-color); margin: 0 0 1rem; }
+.loading, .empty { text-align: center; padding: 2rem; color: var(--p-text-muted-color); }
+.clients-footer { text-align: center; margin-top: 1.5rem; font-size: 0.875rem; }
+.clients-footer a { color: var(--p-primary-color); text-decoration: none; }
+</style>

frontend/src/views/LoginView.vue

@@ -46,6 +46,9 @@
       <div v-if="registrationAllowed" class="auth-footer">
         <router-link to="/register">Noch kein Konto? Registrieren</router-link>
       </div>
+      <div v-if="hasClients" class="auth-footer">
+        <router-link to="/clients"><i class="pi pi-download"></i> Desktop & Mobile Clients herunterladen</router-link>
+      </div>
     </div>
   </div>
 </template>
@@ -68,12 +71,17 @@ const password = ref('')
 const error = ref('')
 const loading = ref(false)
 const registrationAllowed = ref(false)
+const hasClients = ref(false)
 
 onMounted(async () => {
   try {
     const res = await axios.get('/api/auth/registration-status')
     registrationAllowed.value = res.data.allowed
   } catch { registrationAllowed.value = false }
+  try {
+    const res = await axios.get('/api/clients')
+    hasClients.value = res.data.has_clients
+  } catch { hasClients.value = false }
 })
 
 async function handleLogin() {