Refine build cleanup and script variable handling

Updates the build process to remove any existing Apps.iso during cleanup, ensuring a fresh build without stale artifacts.

Clarifies in the app script template that configuration variables are treated as strings. The examples are updated to reflect this, preventing potential errors in custom scripts when checking for boolean-like values.

FFUDevelopment/BuildFFUVM.ps1

@@ -3501,7 +3501,13 @@ function Get-FFUEnvironment {
         Remove-Item -Path $KBPath -Recurse -Force -ErrorAction SilentlyContinue
         WriteLog 'Removal complete'
     }
-    Writelog 'Removing dirty.txt file'
+    # Remove existing Apps.iso
+    if (Test-Path -Path $AppsISO) {
+        WriteLog "Removing $AppsISO"
+        Remove-Item -Path $AppsISO -Force -ErrorAction SilentlyContinue
+        WriteLog 'Removal complete'
+    }
+    WriteLog 'Removing dirty.txt file'
     Remove-Item -Path "$FFUDevelopmentPath\dirty.txt" -Force
     WriteLog "Cleanup complete"
 }