fix: in activate bash output, wrap mise executable path in single-quotes

[cspotcode]

On Windows, the path to mise.exe will contain backslashes.
Both busybox.exe bash and Git-for-Windows' "Git Bash" can understand these backslash paths.
But bash syntax rules dictate that unquoted backslashes are interpreted as escapes. We must wrap the path in single-quotes to avoid this.

# In "Git Bash" or "busybox.exe bash"
# Backslash paths are accepted
$ 'G:\dev\@jdx\mise\target\debug\mise.exe' --version
...
2025.11.5-DEBUG windows-x64 (2025-11-18)

# But unqouted is broken
# because bash's syntax rules will interpret any unquoted backslashes as escapes
$ G:\dev\@jdx\mise\target\debug\mise.exe --version
bash: G:[email protected]: not found

Quoting is technically more correct on Linux, too, even though the issues it avoids -- splitting on spaces -- are largely hypothetical.¹

I can't think of any way that this code change would break someone's legitimate setup on Linux or Mac.

Footnotes

1. To be pedantic, if the path to mise includes a single-quote -- if the name of a parent directory has a single-quote in it -- then this will be broken on Linux, but it would already be broken before this code change, so we are not making it worse. ↩

[cspotcode]

Related: #6993