Add auto-update support (tauri-plugin-updater) and Gitea release pipeline

Ed25519-signed updates, checked via a fixed-tag latest.json manifest on
Gitea Releases; scripts/release.sh automates build+sign+publish. Adds
a manual "Nach Updates suchen" trigger plus a silent startup check.

src/App.tsx

@@ -45,6 +45,7 @@ import { api } from './lib/api'
 import { parseAddressList } from './lib/addresses'
 import { escapeHtml } from './lib/richtext'
 import { loadAppSettings, saveAppSettings, type AppSettings } from './lib/settings'
+import { checkForUpdate, installUpdate } from './lib/updater'
 import {
   applyTheme,
   loadConversationsEnabled,
@@ -253,6 +254,11 @@ export default function App() {
     setTimeout(() => setToast(null), 3500)
   }, [])
 
+  useEffect(() => {
+    handleCheckForUpdates(true)
+    // eslint-disable-next-line react-hooks/exhaustive-deps
+  }, [])
+
   useEffect(() => {
     applyTheme(theme)
     if (theme !== 'system') return
@@ -443,6 +449,25 @@ export default function App() {
     // eslint-disable-next-line react-hooks/exhaustive-deps
   }, [view, selectedMessage])
 
+  async function handleCheckForUpdates(silent = false) {
+    const update = await checkForUpdate()
+    if (!update) {
+      if (!silent) showToast('Du hast schon die neueste Version')
+      return
+    }
+    if (!window.confirm(`Version ${update.version} ist verfügbar (aktuell: ${update.currentVersion}).\n\n${update.body ?? ''}\n\nJetzt installieren? Die App startet danach neu.`)) {
+      return
+    }
+    showToast('Update wird heruntergeladen…')
+    try {
+      await installUpdate(update, (pct) => {
+        if (pct !== null) showToast(`Update wird installiert… ${pct}%`)
+      })
+    } catch (e) {
+      showToast(`Update fehlgeschlagen: ${e}`)
+    }
+  }
+
   function handleRefresh() {
     if (offlineMode) {
       showToast('Offline-Modus aktiv')
@@ -1818,6 +1843,7 @@ export default function App() {
         onSyncGoogleCalendar={handleSyncGoogleCalendar}
         onReconnectGoogleAccount={handleReconnectGoogleAccount}
         onOpenCaldav={() => setCaldavModalOpen(true)}
+        onCheckForUpdates={handleCheckForUpdates}
         theme={theme}
         onThemeChange={handleThemeChange}
         onOpenSettings={() => setSettingsModalOpen(true)}

src/components/Ribbon.tsx

@@ -273,6 +273,7 @@ export function Ribbon({
   onSyncGoogleCalendar,
   onReconnectGoogleAccount,
   onOpenCaldav,
+  onCheckForUpdates,
   theme,
   onThemeChange,
   onOpenSettings,
@@ -337,6 +338,7 @@ export function Ribbon({
   onSyncGoogleCalendar?: (accountId: string) => Promise<void>
   onReconnectGoogleAccount?: (accountId: string) => Promise<void>
   onOpenCaldav?: () => void
+  onCheckForUpdates: () => void
   theme: Theme
   onThemeChange: (t: Theme) => void
   onOpenSettings: () => void
@@ -556,6 +558,7 @@ export function Ribbon({
           <ClassicRibbonGroup caption="Support">
             <HelpMenu onShowShortcuts={onShowShortcuts} />
             <AboutMenu />
+            <ClassicButton icon={RefreshCw} label="Nach Updates suchen" onClick={onCheckForUpdates} />
           </ClassicRibbonGroup>
         )}
       </ClassicRibbonBody>

src/lib/updater.ts

@@ -0,0 +1,27 @@
+import { check, type Update } from '@tauri-apps/plugin-updater'
+import { relaunch } from '@tauri-apps/plugin-process'
+
+export async function checkForUpdate(): Promise<Update | null> {
+  try {
+    return await check()
+  } catch {
+    return null
+  }
+}
+
+export async function installUpdate(update: Update, onProgress: (pct: number | null) => void): Promise<void> {
+  let total = 0
+  let downloaded = 0
+  await update.downloadAndInstall((event) => {
+    if (event.event === 'Started') {
+      total = event.data.contentLength ?? 0
+      onProgress(total > 0 ? 0 : null)
+    } else if (event.event === 'Progress') {
+      downloaded += event.data.chunkLength
+      onProgress(total > 0 ? Math.min(100, Math.round((downloaded / total) * 100)) : null)
+    } else if (event.event === 'Finished') {
+      onProgress(100)
+    }
+  })
+  await relaunch()
+}