Derived from OSIT MasterKey app (LegacyUtilities.m, Ian Kohl 2019). Uses CGConfigureDisplayMirrorOfDisplay — native macOS API, no Homebrew dependency. Handler now tries display_control first; falls back to displayplacer for missing binary or per-device configStr overrides. Build the binary via scripts/build-display-control.sh on a Mac (requires Xcode CLT only), then commit resources/bin/display_control. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>