install.sh: keep the studio launch from draining the curl | sh script (#6258)

When installed via 'curl -fsSL https://unsloth.ai/install.sh | sh', the
shell reads the script from the pipe on stdin. The optional 'start now'
step launches 'unsloth studio' in the foreground, and as a server it
inherits and drains the rest of the piped script from stdin. The shell
then hits EOF partway through the trailing if/case and dies with
'Syntax error: end of file unexpected (expecting fi)' (reported on WSL,
where /bin/sh is dash). Redirect the launch's stdin away from the pipe so
the script stays intact. The server does not read stdin and Ctrl+C still
works via the controlling terminal.

install.sh

@@ -2900,7 +2900,10 @@ if [ -t 1 ]; then
     case "${_reply:-y}" in
         [Yy]*|"")
             step "launch" "starting Unsloth Studio..."
-            "$VENV_DIR/bin/unsloth" studio -p 8888
+            # Detach stdin from the `curl | sh` pipe: as a foreground server the
+            # studio would otherwise drain the rest of this piped script, leaving
+            # the shell to die parsing the now-truncated tail (`unexpected fi`).
+            "$VENV_DIR/bin/unsloth" studio -p 8888 </dev/null
             _LAUNCH_EXIT=$?
             if [ "$_LAUNCH_EXIT" -ne 0 ] && [ "$_MIGRATED" = true ]; then
                 echo ""