Fix restart functionality: use exit code mechanism instead of direct process spawning

[Copilot]

Problem

Restart functionality failed because restart_app() attempted to spawn new processes directly with Windows-specific subprocess code and called sys.exit(0), bypassing the existing EXIT_CODE_RESTART mechanism. This broke packaged builds and non-Windows platforms.

Changes

app/view/main/window.py

• Replaced direct process spawning with QApplication.exit(EXIT_CODE_RESTART)
• Removed Windows-specific subprocess code and unused imports (-28 lines)

main.py

• Enhanced restart_application() with platform-specific logic:
  • Windows: subprocess.Popen() with DETACHED_PROCESS flags
  • Linux/Unix/macOS: os.execl() to replace current process
• Moved subprocess/platform imports to module level

Key change

# Before: window.py tried to restart directly (didn't work)
subprocess.Popen([sys.executable] + args, ...)
sys.exit(0)

# After: window.py signals restart request
QApplication.exit(EXIT_CODE_RESTART)  # main.py handles actual restart

The restart now flows through the proper cleanup and exit handler that checks for EXIT_CODE_RESTART, ensuring resources are released correctly before relaunching.

Original prompt

目前代码“重启”功能有问题，请帮忙修复（确保打包前和打包（actions）后全部正常运行

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