fix(updater): show update errors as a persistent destructive panel

Previously updateStatus.error only appeared in the muted-foreground
paragraph next to the title — easy to miss. With signature failures
and disk-full errors visible only there, users saw the button
re-enable and nothing else and concluded the click did nothing.

Now errors render in a dedicated AlertTriangle-prefixed panel with
destructive styling, showing the raw message in monospace so the
actual cause (ditto, codesign, ENOTFOUND) is copy-pastable.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: beautyfree

src/mainview/i18n/en.ts

@@ -305,6 +305,7 @@ const en = {
     updateStateDownloading: "Downloading update…",
     updateStateReady: "Update ready — restart to install",
     updateStateError: "Update check failed",
+    updateErrorTitle: "Update failed",
     updateCheckNow: "Check for updates",
     updateDownload: "Download update",
     updateRestart: "Restart & install",

src/mainview/pages/Settings.tsx

@@ -10,6 +10,7 @@ import {
   ExternalLink,
   Download,
   RotateCw,
+  AlertTriangle,
 } from 'lucide-react'
 import { openUrl, invoke, listen } from '@/mainview/lib/native'
 import type {
@@ -559,6 +560,24 @@ export default function SettingsPage() {
               )}
             </div>
           </div>
+          {/* Persistent error surface — the inline muted paragraph above was
+           *  too easy to miss. Errors from autoUpdater (signature, disk full,
+           *  network) stay visible here with an explicit destructive style
+           *  until the user runs a successful check/download that clears the
+           *  state. */}
+          {updateStatus?.error && (
+            <div className="flex items-start gap-2 rounded-lg border border-destructive/30 bg-destructive/5 px-3 py-2 text-xs">
+              <AlertTriangle className="mt-0.5 size-3.5 shrink-0 text-destructive" />
+              <div className="min-w-0 flex-1">
+                <p className="font-medium text-destructive">
+                  {t('settings.updateErrorTitle')}
+                </p>
+                <p className="mt-0.5 text-muted-foreground break-words font-mono">
+                  {updateStatus.error}
+                </p>
+              </div>
+            </div>
+          )}
         </section>