fix: don't suggest stacking base branch onto itself (#51)

When running `stack status` on the base branch (e.g., main), the command
would incorrectly offer to add it to a stack with itself as parent.
Accepting this created a circular dependency (main → main).

Now detects when the current branch is the base branch and shows a
helpful message instead of the problematic prompt.

Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>

Author: javoire

cmd/status.go

@@ -143,6 +143,14 @@ func runStatus(gitClient git.GitClient, githubClient github.GitHubClient) error
 	// Check this BEFORE waiting for PR fetch to avoid long delays
 	if tree == nil {
 		baseBranch := stack.GetBaseBranch(gitClient)
+
+		// Don't offer to add the base branch to a stack - it can't have a parent
+		if currentBranch == baseBranch {
+			fmt.Printf("Branch '%s' is the base branch and cannot be part of a stack.\n", ui.Branch(currentBranch))
+			fmt.Printf("\nUse '%s' to create a new stack branch.\n", ui.Command("stack new <branch-name>"))
+			return nil
+		}
+
 		fmt.Printf("Current branch '%s' is not part of a stack.\n\n", ui.Branch(currentBranch))
 		fmt.Printf("Add to stack with '%s' as parent? [Y/n] ", ui.Branch(baseBranch))