ui: Align shortcut handling with ImGui Ctrl/Cmd model

[igorleonovich]

Summary

This PR updates shortcut detection logic to match Dear ImGui’s current input model,
where Ctrl and Cmd are automatically swapped on macOS.

Background

Starting with ImGui v1.92.5, the shortcut modifier handling was simplified:
Ctrl/Cmd mapping on macOS is now handled internally by ImGui, and
ImGuiMod_Shortcut was removed.

As a result, application code no longer needs to special-case macOS
or explicitly check for KeySuper.

What changed

• Removed legacy macOS-specific shortcut branching
• Rely on Ctrl as the canonical cross-platform shortcut modifier
• Preserve existing behavior by rejecting Alt/Shift for plain shortcuts

References

• Dear ImGui v1.92.5 release notes
• Commit: “Inputs: swap Ctrl and Cmd on macOS X, remove ImGuiMod_Shortcut”
  ocornut/imgui@7747106

[mborgerson]

Thanks!