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/nb.ts

@@ -350,6 +350,18 @@ export const nbTranslation = {
     updaterAvailable: 'Ny versjon er tilgjengelig',
     updaterVersion: 'v{{version}} er tilgjengelig',
     updaterWebsite: 'Nettsted',
+    updaterModalTitle: 'Ny versjon tilgjengelig',
+    updaterChangelog: 'Hva er nytt',
+    updaterDownloadBtn: 'Last ned nå',
+    updaterSkipBtn: 'Hopp over denne versjonen',
+    updaterRemindBtn: 'Påminn meg senere',
+    updaterDone: 'Nedlasting fullført',
+    updaterShowFolder: 'Vis i mappe',
+    updaterInstallHint: 'Lukk Psysonic og kjør installasjonsprogrammet manuelt.',
+    updaterAurHint: 'Installer oppdateringen via AUR:',
+    updaterErrorMsg: 'Nedlasting mislyktes',
+    updaterRetryBtn: 'Prøv igjen',
+    updaterOpenGitHub: 'Åpne på GitHub',
   },
   settings: {
     title: 'Innstillinger',