Initial extraction: C++ MixerEngine standalone daemon

Extracted from op-pedal mixer-engine branch. Core components:

- MixerEngine / MixerChannelStrip / MixerBus — cleaned of LV2/Pedalboard/IHost/MidiMapper deps
- MixerControlServer — Unix domain socket JSON control interface
- main.cpp — JACK audio I/O client with headless fallback
- CMake build — auto-fetches nlohmann/json, links JACK
- 9 core tests passing

Architecture: JACK ports → MixerEngine::process() → JACK ports,
controlled via Unix socket JSON commands.

build/CMakeFiles/InstallScripts.json

@@ -0,0 +1,8 @@
+{
+	"InstallScripts" : 
+	[
+		"/home/oplabs/projects/oplabs-mixer-daemon/build/cmake_install.cmake",
+		"/home/oplabs/projects/oplabs-mixer-daemon/build/_deps/nlohmann_json-build/cmake_install.cmake"
+	],
+	"Parallel" : false
+}