[codex] Add macOS native menu shortcuts

[gjxwxt]

What changed

• added a macOS native application menu with Cmd+H mapped to hide the app windows
• added a macOS window menu entry with Cmd+W mapped to hide the active window
• kept Cmd+Q as an explicit application quit action
• added localized menu strings for the new macOS menu entries

Why

The macOS build only registered a minimal native menu, so standard macOS shortcuts like Cmd+H, Cmd+W, and Cmd+Q were not fully wired into the application lifecycle.

Impact

macOS users now get the expected shortcut behavior:

• Cmd+H hides the app windows
• Cmd+W hides the current window instead of acting like quit
• Cmd+Q still exits the app

Root cause

The app-level NativeMenu only exposed Settings and Exit, and the main window behavior relied on close interception rather than native macOS menu shortcut bindings.

Validation

• inspected the macOS Avalonia menu and window lifecycle code paths
• ran git diff --check
• attempted dotnet build src/BD.WTTS.Client.Avalonia.App/BD.WTTS.Client.Avalonia.App.csproj, but dotnet is not installed in this environment