fix: prevent Bubble Tea spinner hang in non-TTY environments

Add TTY check before starting the Bubble Tea spinner to prevent potential
hangs in CI environments where no terminal is available.

The issue was that tea.Program.Run() could block indefinitely when trying
to initialize the terminal in non-TTY environments like CI runners.

This fix adds isTTY() check at the start of the spinner, similar to how
info.go already handles TTY detection for its version fetch spinner.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: aknysh

toolchain/install_helpers.go

@@ -27,11 +27,18 @@ type installResult struct {
 }
 
 // startSpinner starts a spinner with the given message.
+// Spinner is only started if we're in a TTY environment.
 func (sc *spinnerControl) start(message string) {
 	if !sc.showingSpinner {
 		return
 	}
 
+	// Don't start Bubble Tea spinner in non-TTY environments (CI, piped output).
+	// This prevents potential hangs when tea.Program.Run() blocks on terminal init.
+	if !isTTY() {
+		return
+	}
+
 	sc.program = runBubbleTeaSpinner(message)
 	go func() {
 		// Run spinner in background, ignore error since program is managed by quit channel.