refactor: simplify project directory name normalization

[zimeg]

Changelog

Project directory names now preserve original casing and path-safe characters (underscores, dots) instead of forcing kebab-case.

Summary

This pull request simplifies how slack create normalizes project directory names. Previously, all non-alphanumeric characters were replaced with dashes and the name was forced to lowercase. Now:

• Spaces are replaced with dashes
• Shell-unsafe characters (!@#$%^&*(){}[]|;:'"<>?~ etc.) are removed
• Path-safe characters (letters, digits, -, _, .) are preserved as-is
• Original casing is preserved

Preview

Before: slack create "My_Cool.App" → directory my-cool-app
After: slack create "My_Cool.App" → directory My_Cool.App

Testing

• Run slack create "My Cool App" and verify the directory is named My-Cool-App
• Run slack create "my_app.test" and verify underscores and dots are preserved
• Run slack create "app!@#name" and verify unsafe characters are removed → appname

Notes

This is a less opinionated default — we can always tighten restrictions later if needed.

Requirements

• I've read and understood the Contributing Guidelines and have done my best effort to follow them.
• I've read and agree to the Code of Conduct.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 71.70%. Comparing base (c693443) to head (31fdead).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #559      +/-   ##
==========================================
+ Coverage   71.66%   71.70%   +0.04%     
==========================================
  Files         226      226              
  Lines       19115    19114       -1     
==========================================
+ Hits        13699    13706       +7     
+ Misses       4209     4205       -4     
+ Partials     1207     1203       -4     

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