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/en.ts

@@ -351,6 +351,18 @@ export const enTranslation = {
     updaterAvailable: 'Update available',
     updaterVersion: 'v{{version}} is available',
     updaterWebsite: 'Website',
+    updaterModalTitle: 'New Version Available',
+    updaterChangelog: "What's New",
+    updaterDownloadBtn: 'Download Now',
+    updaterSkipBtn: 'Skip this Version',
+    updaterRemindBtn: 'Remind me Later',
+    updaterDone: 'Download complete',
+    updaterShowFolder: 'Show in Folder',
+    updaterInstallHint: 'Close Psysonic and run the installer manually.',
+    updaterAurHint: 'Install the update via AUR:',
+    updaterErrorMsg: 'Download failed',
+    updaterRetryBtn: 'Retry',
+    updaterOpenGitHub: 'Open on GitHub',
   },
   settings: {
     title: 'Settings',
@@ -479,6 +491,7 @@ export const enTranslation = {
     aboutLicense: 'License',
     aboutLicenseText: 'GNU GPL v3 — free to use, modify, and distribute under the same license.',
     aboutRepo: 'Source Code on GitHub',
+    aboutPreviewUpdate: 'Preview Update Modal',
     aboutVersion: 'Version',
     aboutBuiltWith: 'Built with Tauri · React · TypeScript · Rust/rodio',
     aboutAiCredit: 'Developed with the support of Claude Code by Anthropic',