fix: handle error return values to pass linter

Fix errcheck linter warnings:
- Handle cmd.Help() error in rootCmd
- Handle gitCmd.Run() error in listCmd

Both errors are intentionally ignored as they don't affect
functionality in these contexts.

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

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

Author: timvw

main.go

@@ -36,7 +36,7 @@ var rootCmd = &cobra.Command{
 Worktrees are organized at: ` + worktreeRoot + `/<repo>/<branch>
 Set WORKTREE_ROOT to customize the location.`,
 	Run: func(cmd *cobra.Command, args []string) {
-		cmd.Help()
+		_ = cmd.Help()
 	},
 }
 
@@ -274,7 +274,7 @@ var listCmd = &cobra.Command{
 		gitCmd := exec.Command("git", "worktree", "list")
 		gitCmd.Stdout = os.Stdout
 		gitCmd.Stderr = os.Stderr
-		gitCmd.Run()
+		_ = gitCmd.Run()
 	},
 }