Fix install.bat failing when the user profile path contains a space (#1854)

`mkdir %tmp_dir% 2>nul` is unquoted, so when %USERPROFILE% contains a
space cmd splits it into two arguments and creates the wrong directories.
The error is swallowed by 2>nul, so the script continues with a tmp
directory that was never created, and the download then fails with a bare
`curl: (23) client returned ERROR on write of 16384 bytes`.

Every other use of the path variables in this file is already quoted.

Co-authored-by: Claude Opus 5 <noreply@anthropic.com>

Author: djantea

public/install.bat

@@ -100,7 +100,7 @@ if "%elixir_major_minor%" == "1.14" (
 
 set "root_dir=%USERPROFILE%\.elixir-install"
 set "tmp_dir=%root_dir%\tmp"
-mkdir %tmp_dir% 2>nul
+mkdir "%tmp_dir%" 2>nul
 set "otp_dir=%root_dir%\installs\otp\%otp_version%"
 set "elixir_dir=%root_dir%\installs\elixir\%elixir_version%-otp-%elixir_otp_release%"