release: Refactor quickmenu mod checks and callbacks

Clean up and restructure the mod presence checks in hooks/quickmenu.lua. Replace commented-out branches with explicit comparisons (== false) for WeaponLib and LMG Steelsights, standardize QuickMenu creation formatting, and show the appropriate menus when mods are missing. Fix the download button callback by wrapping os.execute in a function so it runs only when clicked (previous code executed immediately). Overall improves readability and corrects callback behavior.