package_mac: expand the utmctl scripting target before signing

[LayerTM]

In a package built with scripts/package_mac.sh unsigned, every utmctl command fails, although AppleScript to the same running UTM works.

Steps

1. Build with ./scripts/build_utm.sh -k macosx -s macOS -a arm64 -o out and package with ./scripts/package_mac.sh unsigned out.xcarchive pkg.
2. Install the app, open UTM, run UTM.app/Contents/MacOS/utmctl list.

Result

warning: failed to get scripting definition from /Applications/UTM.app; it may not be scriptable.
*** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[SBApplication virtualMachines]: unrecognized selector sent to instance …'

Exit code 134. osascript -e 'tell application "/Applications/UTM.app" to get name of every virtual machine' works in the same state.

Cause and fix
utmctl's scripting-targets entitlement names the target app as a dictionary key built from $(PRODUCT_BUNDLE_PREFIX:default=com.utmapp). Xcode expands it only when it signs; package_mac.sh re-signs utmctl from a copy of the raw file, so in an unsigned package the key stays literal and utmctl is not allowed to script UTM at all.

This replaces the build-setting reference with the script's PRODUCT_BUNDLE_PREFIX in the copied utmctl entitlements before signing. It runs in every mode; for signed modes the value is the same one Xcode would have produced.

The app-group strings in macOS-unsigned.entitlements and QEMUHelper-unsigned.entitlements carry the same kind of literal, but they match each other, so UTM and the helper still share the group; changing them would move the group container of existing unsigned installs, so they are left as they are.

Tested: after packaging, codesign -d --entitlements - --xml UTM.app/Contents/MacOS/utmctl shows the target com.utmapp.UTM, codesign --verify --deep --strict passes, and utmctl start / utmctl status work against a running unsigned UTM on macOS 26 (before the change both failed as described above).