fix: support scaffolding into current directory with .

[technophile-04]

Summary

Closes #402

• npx create-eth . now scaffolds into the current directory instead of failing with mkdir: .: File exists
• If the directory is not empty, it throws a clear error: Directory /path is not empty
• Skips the cd . instruction in the outro message when . is used

How it works

When the target directory already exists (e.g. .), we skip mkdir and instead check if the directory is empty. If it contains any files, we error out to prevent overwriting existing projects.

This follows the same approach as create-next-app, which also supports . as the project path and checks for an empty directory before proceeding.

Test plan

• create-eth . in an empty directory → scaffolds successfully
• create-eth . in a non-empty directory → errors with "Directory is not empty"
• create-eth my-project → works as before (unchanged path)

🤖 Generated with Claude Code

[rin-st]

Not sure how to test with empty . folder without release, but all other cases works well, especially installing to random empty folder which I think is almost the same as empty . folder