ci: explicit GUID for the Start Menu component (CNDL0230)

candle rejected auto-GUID '*' on StartMenuShortcut: a component mixing a
File and a RegistryValue keypath can't have one auto-generated. Assign a
fixed GUID (the canonical WiX shortcut-component shape).

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>