feat: Add vanilla sound selection functionality

[Sweatent]

• Add UIVanillaSoundOverlayPanel for selecting vanilla Minecraft sounds
• Integrate vanilla sound selection into UISoundOverlayPanel with right-click context menu
• Add visual hint when sound list is empty to guide users
• Automatically copy selected vanilla sounds to mod's audio directory
• Refresh sound list after adding vanilla sounds
• Add necessary localization keys for UI text
• Format code and add concise comments for better maintainability"

[mchorse]

I checked it, and it doesn't appear to work in development or in Modrinth or MultiMC launchers. I don't think this is acceptable for me. I'll keep the pull request open. Maybe you'll find a way to find another way to load those sounds (for example through ResourceManager system) or find a way to recursively search for assets/index/ folder.