refactor: use the new utils.ps1 script for operations

01-essentials/05-cherry-pick/setup.ps1

@@ -10,6 +10,8 @@
     the bug fixes to the main branch.
 #>
 
+. "$PSScriptRoot\..\..\util.ps1"
+
 # Remove existing challenge directory if present
 if (Test-Path "challenge") {
     Write-Host "Removing existing challenge directory..." -ForegroundColor Yellow
@@ -42,11 +44,7 @@ git add app.py
 git commit -m "Initial app implementation" | Out-Null
 
 # Detect the main branch name after first commit
-$mainBranch = git branch --show-current
-if (-not $mainBranch) {
-    $mainBranch = git config --get init.defaultBranch
-    if (-not $mainBranch) { $mainBranch = "main" }
-}
+$mainBranch = Get-MainBranch
 Write-Host "Default branch detected: $mainBranch" -ForegroundColor Yellow
 
 $readme = @"