[BUG] Installer can delete unrelated `strix` executables from `PATH`

Summary

The shell installer can delete existing strix executables outside its own installation directory, including files managed by pipx or another development environment

Code paths involved

check_existing_installation enumerates matches from which -a strix and removes regular files or symlinks

verify_installation may remove another executable when it wins path resolution

The installer can also call pipx uninstall strix-agent based on the discovered path

This report comes from source tracing rather than running the destructive path

Why this is risky

Path discovery shows that another executable exists, but it does not establish that the installer owns that file

Removing the file automatically can break a setup the user intended to keep

Requested behavior

The installer should replace only the executable inside its managed directory

If another strix wins path resolution, report its location and explain how the user can resolve the conflict

Do not delete that file or invoke pipx uninstall without an explicit user action

A regression test can model several strix executables on PATH and confirm that only the managed path changes