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

Source/Params.h

@@ -10,10 +10,11 @@ enum class Id : int {
     fenvA,    fenvD,      fenvS,      fenvR,
     lfoRate,  lfoShape,   lfoDepth,   lfoTarget,
     fxType,   fxAmt,      fxTime,
-    vol,      pan,        poly,       glide, tune
+    vol,      pan,        poly,       glide, tune,
+    hq
 };
 
-constexpr int num = 29;
+constexpr int num = 30;
 
 struct Desc {
     const char* id;
@@ -38,4 +39,9 @@ const char* lfoShapeName (int s);
 const char* lfoTargetName (int t);
 const char* fxTypeName (int t);
 
+constexpr int delaySyncCount = 11;
+const char* delaySyncName (int s);              // "OFF", "1/16", ...
+double delaySyncBeats (int s);                  // beat multiple for sync delay
+float  delaySyncMaxTime();                      // max delay seconds needed for slow sync
+
 } // namespace prm