feat(desktop): add "Reset Zoom" item to the Window menu - #5185

Closes #5184

Summary

Add a Reset Zoom item to the Window menu, between "Zoom Out" and the separator.
It restores the window zoom factor to 1.0 by reusing the existing mt::window-zoom
IPC channel (same workaround as Zoom In/Out for Electron#16018), and is registered
as a window.resetZoom command so it can be rebound in preferences.

• New action: resetZoom in src/main/windows/utils.ts
• New command id: WINDOW_ZOOM_RESET (window.resetZoom) in src/common/commands/constants.ts
• Menu entry added in src/main/menu/templates/window.ts with i18n labels
  (menu.window.resetZoom) for all 10 locales

Type of change

• Bug fix (non-breaking, fixes an issue)
• New feature (non-breaking, adds functionality)
• Breaking change (causes existing functionality to change)
• Documentation update

Test plan

• New tests added (or explain why not needed) - not needed: follows the exact
  pattern of the existing Zoom In/Out menu items; behavior verified by typecheck
  and manual testing.
• Manually tested on:

Notes for reviewers [optional]

• No default accelerator is assigned. Ctrl+0/Cmd+0 are already taken
  (tabs.switchToTenth on Win/Linux, paragraph.paragraph on macOS), so the
  keybinding ships empty like window.zoomIn/window.zoomOut and can be
  customized in preferences.
• Reset always targets 1.0, matching Electron's built-in resetZoom role behavior.

By submitting this pull request, I confirm that my contribution is made under the terms of the MIT license.