feat: use native macOS window frame on Apple Silicon

[ZiWei09]

Summary

This PR replaces the Windows-style custom titlebar and resize borders with the native macOS window frame on Q_OS_DARWIN. The custom FramelessWindowHint approach looks out of place on macOS and causes usability issues.

Changes

• DSView/pv/mainframe.cpp: On macOS, use Qt::Window instead of FramelessWindowHint, skip creating TitleBar and Border widgets, use QGridLayout directly for the main window
• DSView/pv/mainwindow.cpp: Add #ifndef Q_OS_DARWIN guard for title_bar assertion since it's NULL on macOS

Tested

• macOS 15 (Apple Silicon, arm64 native build)
• Windows/Linux behavior is unchanged (all changes are guarded by #ifdef Q_OS_DARWIN)

Screenshot

Before: Custom Windows-style titlebar with DSL logo, minimize/maximize/close buttons
After: Native macOS window frame with standard traffic light buttons and proxy icon

---

This addresses the request for native macOS arm64 builds (see v1.3.2-arm64 release with prebuilt .dmg at https://github.com/ZiWei09/DSView/releases).

[oxoocoffee]

I did try your build and dropped it to ~/Applications/DSView.app. Since the application is not signed it is failing to start. But running sudo xattr -r -d com.apple.quarantine ~/Applications/DSView.app which should do the trick, I get following

 sudo xattr -r -d com.apple.quarantine ~/Applications/DSView.app
xattr: No such file: /Users/rob/Applications/DSView.app/Contents/Frameworks/Python.framework/Versions/3.14/lib/python3.14/site-packages

 $ ls -l /Users/rob/Applications/DSView.app//Contents/Frameworks/Python.framework/Versions/3.14/lib/python3.14/ | grep site-packages
lrwxr-xr-x@   1 rob  staff      46 May 15 13:43 site-packages -> ../../../../../../lib/python3.14/site-packages

 $ ls -l  /Users/rob/Applications/DSView.app//Contents/Frameworks/Python.framework/Versions/3.14/lib/python3.14/site-packages/
ls: /Users/rob/Applications/DSView.app//Contents/Frameworks/Python.framework/Versions/3.14/lib/python3.14/site-packages/: No such file or directory

$ python3 --version 
Python 3.14.5

[ZiWei09]

Thanks for the detailed report! This is a build system issue — when the Python.framework is copied into the app bundle, a relative symlink (site-packages -> ../../../../../../lib/python3.14/site-packages) is preserved from the Homebrew installation, but the target directory (Contents/lib/python3.14/site-packages) isn't included in the bundle. This causes both codesign and xattr to fail.
Quick Fix For Nowå
You can resolve this temporarily by running the following commands in your terminal:

sudo rm /Applications/DSView.app/Contents/Frameworks/Python.framework/Versions/3.14/lib/python3.14/site-packages
sudo mkdir /Applications/DSView.app/Contents/Frameworks/Python.framework/Versions/3.14/lib/python3.14/site-packages
sudo codesign --force --deep --sign - /Applications/DSView.app
sudo xattr -r -d com.apple.quarantine /Applications/DSView.app
open /Applications/DSView.app

I'll also fix this in the build system so future builds handle the broken symlinks automatically.