[eagleoflqj]

Use a single SwiftUI Window scene and disable automatic window tabbing during launch. Remove the New Window, New Tab, Show Tab Bar, and Merge All Windows menu entries; Command-N and Command-T no longer create additional windows or tabs.

Launch the app smoke test through NSWorkspace.openApplication with a separate application instance, so it exercises normal macOS app launching and works while another SimStore instance is running. Preserve the existing exit-after-closing-the-last-window behavior.

Validation:

• CMake/Ninja Release build and strict Swift formatting checks passed.
• All four CTest checks passed, including app launch and close-to-quit behavior.
• Native GUI verification confirmed one visible main window, disabled tabbing, no window/tab creation menu entries, and no extra windows after Command-N or Command-T.