fix: bring window to front when opening .md file via Finder on macOS

[dongyccc]

Summary

Fixed a bug where double-clicking a .md file in Finder on macOS loads the file content silently without bringing the milkup window to the foreground. Users have to manually click the app icon in the Dock to see the window.

Root Cause

The open-file event handler (src/main/index.ts:292) calls sendFileToRenderer() which sends file data to the renderer via IPC, but never calls focus() / show() / restore() on the window.

In contrast, the second-instance handler (line 280) and activate handler (line 320) both correctly activate the window before processing.

Fix

Added 3 lines in sendFileToRenderer's sendFile closure to mirror the window activation logic already present in second-instance:

if (targetWin.isMinimized()) targetWin.restore();
if (!targetWin.isVisible()) targetWin.show();
targetWin.focus();

Affected Scenarios

Scenario	Before	After
Cold launch (double-click .md, app not running)	Window may stay behind	✅ Window comes to front
App running, window hidden (red close button on macOS)	Content loaded, window stays hidden	✅ Window shown + focused
App running, window minimized	Content loaded, stays minimized	✅ Window restored + focused
App in foreground, double-click another .md	Works fine	✅ No change

Tested

• macOS arm64 (Apple Silicon) with macOS 26
• Built and installed locally, verified fix resolves the issue

[LarryZhu-dev]

@dongyccc 感谢贡献

[github-actions]

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