fix: allow project creation in directories with only .git folder

[saseungmin]

Summary

Problem

Currently, the library validation prevents creating projects in directories that contain any files, including .git folders. This creates a frustrating user experience when:

1. Users clone an empty GitHub repository
2. The directory contains only a .git folder
3. The validation fails with "Directory already exists" error

This is a common workflow where developers create a GitHub repo first, then clone it locally to set up their React Native library.

Solution

• Treat directories as "empty" if they contain no files OR only a .git folder
• Allow project creation in such directories

This follows the same pattern used by Vite's create-vite tool:

• Vite source code

Test plan

1. yarn install
2. cd packages/create-react-native-library
3. yarn prepare
4. run ./bin/create-react-native-library

Tested scenarios:

• Empty directory - works as before
• Directory with only .git - now works ✅
• Directory with other files - still blocked as expected
• Non-existent directory - works as before