Add auto-update functionality with electron-updater

[Copilot]

Implements automatic update checking and installation for WhispLine using electron-updater with GitHub Releases as the update distribution mechanism.

Changes

• Auto-updater service (src/auto-updater-service.js)

  • Event-driven update lifecycle management
  • User dialogs for update available, download progress, and installation
  • Throttled progress logging (10% intervals) to prevent log spam
  • Disabled in development mode

• Main process integration (src/main.js)

  • "Check for Updates" menu item in system tray
  • Silent update check 5s after app startup (production only)
  • Configurable via UPDATE_CHECK_DELAY_MS constant

• GitHub Actions release workflow (.github/workflows/release.yml)

  • Multi-platform builds (macOS arm64, Windows, Linux) triggered on version tags
  • Explicit GITHUB_TOKEN permissions (contents: read for builds, contents: write for releases)
  • Specific artifact patterns (.dmg, .exe, .AppImage, .yml only)

• Dependencies

  • electron-updater@6.7.3 - update client
  • electron-log@5.4.3 - logging infrastructure

• Configuration (package.json)

  • Publish target: GitHub Releases (hellotaotao/WhispLine)
  • autoDownload: false - requires user consent
  • autoInstallOnAppQuit: true - installs on next quit after download

Security

• Fixed actions/download-artifact CVE (arbitrary file write) by pinning to v4.1.3
• Least-privilege GITHUB_TOKEN permissions in workflow
• CodeQL scan: 0 alerts

Release workflow

git tag v1.0.75
git push origin v1.0.75
# GitHub Actions builds all platforms and publishes to releases
# Users notified on next app launch

Original prompt

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This section details on the original issue you should resolve

<issue_title>App auto-update</issue_title>
<issue_description></issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes App auto-update #2

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