Better Error Feedback & File System Complete

I finished implementing Better Error Feedback and the new file system for CodeKids IDE.
Error messages are now much more beginner-friendly, helping users understand what went wrong instead of only showing technical errors. For common mistakes, the editor now provides simple explanations and helpful suggestions. For example, if a user tries to use a variable before creating it, CodeKids IDE will display a message like:
You used the variable x before creating it. Create it first, for example: x = 10.
I also completed the new file system, which now supports creating multiple files and folders, as well as importing Python files from one another. This makes it much easier to organize projects and gives users a more realistic development experience while keeping the interface simple for beginners.
To make the editor more enjoyable to use, I also added theme support, allowing users to switch between different editor themes.
These features are important milestones for Version 2 and bring CodeKids IDE one step closer to becoming a complete learning environment for new programmers.