feat(updater): professional update modal with skip, changelog, and OS-aware downloader

Replaces the small corner toast with a centered modal that appears on
startup when a newer GitHub release is detected (4 s delay).

Features:
- Skip this Version: stores skipped tag in localStorage, reappears only
  for newer releases
- Collapsible changelog: renders GitHub release body as markdown accordion
- OS-aware download: Windows → .exe installer, macOS → .dmg (aarch64
  preferred), Linux Arch → AUR hint (yay/pacman), Linux other → .AppImage/.deb
- In-app downloader: Rust download_update command streams to ~/Downloads/,
  emits update:download:progress every 250 ms for a real-time progress bar
- Post-download: Show in Folder button opens Downloads dir via shell.open
- Buttons: Download Now / Skip this Version / Remind me Later

Rust: check_arch_linux() reads /etc/arch-release + /etc/os-release
platform.ts: adds IS_MACOS, IS_WINDOWS alongside existing IS_LINUX
Settings About: Preview Update Modal button for testing
Fixes: renderInline regex had nested capture group causing undefined entries
in split() result → TypeError → React crash → WebKit white-screen freeze

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/locales/de.ts

@@ -350,6 +350,18 @@ export const deTranslation = {
     updaterAvailable: 'Update verfügbar',
     updaterVersion: 'v{{version}} verfügbar',
     updaterWebsite: 'Website',
+    updaterModalTitle: 'Neue Version verfügbar',
+    updaterChangelog: 'Was ist neu',
+    updaterDownloadBtn: 'Jetzt herunterladen',
+    updaterSkipBtn: 'Version überspringen',
+    updaterRemindBtn: 'Später erinnern',
+    updaterDone: 'Download abgeschlossen',
+    updaterShowFolder: 'Im Ordner anzeigen',
+    updaterInstallHint: 'Psysonic schließen und das Installationsprogramm manuell ausführen.',
+    updaterAurHint: 'Update über AUR installieren:',
+    updaterErrorMsg: 'Download fehlgeschlagen',
+    updaterRetryBtn: 'Erneut versuchen',
+    updaterOpenGitHub: 'Auf GitHub öffnen',
   },
   settings: {
     title: 'Einstellungen',