Add delay tempo sync, rack faceplate, README, docs

- Add host-tempo-synced delay: FX screen gains a 4th SYNC row for
  rhythmic divisions (1/16 .. 1/1) that lock delay time to DAW tempo
- Embed rack faceplate background (b2.png) via juce binary data
- Add offline dev probe (rmx_probe) for GUI-less MIDI testing
- Allow overriding JUCE_ROOT when configuring the build
- Write comprehensive README describing the instrument, UI, MIDI, DSP,
  and build/install steps

CMakeLists.txt

@@ -54,10 +54,12 @@ message(STATUS "RMX-19 build: ${BUILD_GIT_BRANCH} ${BUILD_GIT_COMMIT}${BUILD_GIT
 # ---------------------------------------------------------------------------
 # JUCE
 # ---------------------------------------------------------------------------
-if(EXISTS "$ENV{HOME}/JUCE/CMakeLists.txt")
-  set(JUCE_ROOT "$ENV{HOME}/JUCE")
-elseif(EXISTS "/opt/JUCE/CMakeLists.txt")
-  set(JUCE_ROOT "/opt/JUCE")
+if(NOT DEFINED JUCE_ROOT)
+  if(EXISTS "$ENV{HOME}/JUCE/CMakeLists.txt")
+    set(JUCE_ROOT "$ENV{HOME}/JUCE")
+  elseif(EXISTS "/opt/JUCE/CMakeLists.txt")
+    set(JUCE_ROOT "/opt/JUCE")
+  endif()
 endif()
 
 if(NOT DEFINED JUCE_ROOT OR NOT EXISTS "${JUCE_ROOT}/CMakeLists.txt")
@@ -92,15 +94,42 @@ set(RMX19_SOURCES
   Source/Params.cpp
 )
 
+juce_add_binary_data(RMX19_Assets
+  NAMESPACE BinaryData
+  SOURCES
+    b2.png
+)
+
 target_sources(RMX19 PRIVATE ${RMX19_SOURCES})
 target_include_directories(RMX19 PRIVATE
   "${CMAKE_CURRENT_SOURCE_DIR}/Source"
   "${CMAKE_CURRENT_BINARY_DIR}/Source")
 
 target_link_libraries(RMX19 PRIVATE
+  RMX19_Assets
   juce::juce_audio_utils
   juce::juce_gui_basics
   juce::juce_dsp)
 
 target_compile_definitions(RMX19 PRIVATE JUCE_MODAL_LOOPS_PERMITTED=1
-  JUCE_VST3_CAN_REPLACE_VST2=0)
+  JUCE_VST3_CAN_REPLACE_VST2=0)
+
+# ---------------------------------------------------------------------------
+# Offline probe (dev only): runs the processor with scripted MIDI, no GUI.
+# ---------------------------------------------------------------------------
+add_executable(rmx_probe Source/Probe.cpp
+  Source/PluginProcessor.cpp
+  Source/PluginEditor.cpp
+  Source/LcdPanel.cpp
+  Source/PresetBank.cpp
+  Source/SynthEngine.cpp
+  Source/Params.cpp)
+target_include_directories(rmx_probe PRIVATE
+  "${CMAKE_CURRENT_SOURCE_DIR}/Source"
+  "${CMAKE_CURRENT_BINARY_DIR}/Source"
+  "${CMAKE_CURRENT_BINARY_DIR}/juce_binarydata_RMX19_Assets/JuceLibraryCode")
+target_link_libraries(rmx_probe PRIVATE
+  RMX19_Assets
+  juce::juce_audio_utils
+  juce::juce_gui_basics
+  juce::juce_dsp)