build(display): universal binary — compile x86_64 + arm64 and lipo into fat binary

Compiles both arches separately then links with lipo -create.
Prevents silent failure when a binary built on Apple Silicon is deployed
to Intel venue Macs (MacBook Air 2018 fleet).

README.md

@@ -363,6 +363,9 @@ xcode-select --install
 # From the repo root:
 ./scripts/build-display-control.sh
 
+# The script compiles x86_64 and arm64 separately then links a universal binary.
+# Expected output at the end: x86_64 arm64
+
 # Test with a second display connected:
 ./resources/bin/display_control status
 ./resources/bin/display_control extend