Improve .gitignore for Python and IDE files

[shahabRDZ]

Summary

• Add Python-specific ignore patterns for the playable_demo/ directory
• Add OS files (.DS_Store, Thumbs.db)
• Add IDE ignore patterns (.vscode, .idea)

Closes #1 (partial)

Test plan

• Verify no tracked files are affected by new ignore rules

[shahabRDZ]

The new ignore patterns are well-organized and cover the Python demo, OS artifacts, and IDE config files. This prevents accidental commits of generated files.

Suggestion: consider adding *.log to catch Unity log files as well.