Add auto-update functionality using electron-updater

[Copilot]

Implements automatic application updates via GitHub Releases using electron-updater.

Changes

• Auto-updater service (src/auto-updater.js): Encapsulates update lifecycle - checking, downloading, installing. Dialogs require user consent for downloads. Auto-installs on app quit.

• Main process integration: Initializes updater post-window creation (production only). Adds IPC handler and menu item for manual checks. 3s startup delay for non-intrusive background checking.

• UI: Refresh icon button next to version number in sidebar. Triggers manual update check on click.

• Configuration: package.json now includes GitHub publish target for electron-builder:

  "publish": [{
    "provider": "github",
    "owner": "hellotaotao",
    "repo": "WhispLine"
  }]

Behavior

Development mode (--dev): Auto-updater disabled entirely.

Production builds: Silent check on startup → user prompt if update available → download → prompt to restart → install on quit.

Dependencies

• electron-updater@6.7.3 - Update management
• electron-log@5.2.4 - Logging for update operations

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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