feat: export modpack mod list to JSON file

[leavraell]

Hi, this is my first contribution. I'm using StoryForge on macOS and found the clipboard-only export limitation so put together a fix. Happy to adjust anything that doesn't fit the project conventions.

Summary

• Add ability to export a modpack's mod list to a JSON file via native save dialog
• Exported mods are sorted alphabetically and include display name for readability
• Accessible from the installation context menu and installation row

Test plan

• Tested locally — export saves a valid JSON file with sorted mod list
• Verify native save dialog works on Windows/Linux

Details

• New utility functions in src/lib/utils.ts for file export
• Rust backend updated in src-tauri/src/modules/utils.rs and lib.rs
• CHANGELOG.md updated

[LovelessCodes]

Hey Leavraell, it looks to me like there's something odd going on here.
It seems you've opened two pull requests for the same thing? 😄