Improves FFU deployment menu selections and device naming

Refactors the `ApplyFFU.ps1` script to use a new `Read-MenuSelection` function for standardized user prompts, improving input validation and allowing users to skip optional prompts (like prefix selection, AP JSON, and PPKG files). Updates sample unattend XML files to use `*` for the computer name, falling back to default Windows naming if not specified. Updates the documentation to reflect the new UI and script behaviors.

docs/quickstart.md

@@ -207,6 +207,12 @@ Use this option when you want a static device name or a template such as `Comp-%
 
 This option writes `prefixes.txt` from the list in the UI. Enter one prefix per line or import an existing prefixes file. The source file can use any name because the UI tracks the prefixes path separately. If there is one prefix, deployment uses it automatically. If there are multiple prefixes, the technician is prompted to select one and the serial number is appended to that prefix.
 
+{: .note-title}
+
+> Note
+>
+> If the technician skips prefix selection when multiple prefixes are available, `ApplyFFU.ps1` leaves the existing unattend `ComputerName` value unchanged. With the current unattend samples set to `<ComputerName>*</ComputerName>`, Windows falls back to its default random computer-name behavior, typically resulting in a name such as `WIN-*`.
+
 {: .warning-title}
 
 > Warning