Add new track copy item actions

[lsooxlla8]

Summary

• add three related item actions as one ReaPack package
• support selected items and media-item Razor Edits with copy/move variants
• reorganize the repository README into package categories

Verification

• Lua syntax parsed for all new scripts and mock test
• selected-item copy, zero-offset copy, and move scenarios pass
• Razor Edit zero-offset copy and move scenarios pass
• git diff --check passes