chore: land janitor round 1 and graft integration

Round 1 findings and fixes, all previously uncommitted:
- FXProcessor per-slot DSP history repair (HEAD does not compile without it)
- SynthVoice::getModulationValue, editor control-lock guard
- ExactCompare.h naming the deliberate exact float comparisons
- KnobLookAndFeel replacing the never-installed SerumLookAndFeel
- 55 first-party compiler warnings to 0
- AGENT.md renamed to AGENTS.md across Source/
- graft repository context graph and its hooks
- JANITOR_TASKS.md and UI_UX_AUDIT.md records

Source/GUI/WaveformDisplay.h

@@ -1,6 +1,7 @@
 #pragma once
 
 #include <JuceHeader.h>
+#include "../ExactCompare.h"
 #include "../Resources.h"
 #include "../Wavetable.h"
 
@@ -15,7 +16,7 @@ class WaveformDisplay : public juce::Component
 public:
     void setWavetables (const WavetableLibrary* lib) { if (wtLib != lib) { wtLib = lib; repaint(); } }
     void setWaveIndex (int index) { if (wave != index) { wave = index; repaint(); } }
-    void setFramePosition (float pos) { if (wtPos != pos) { wtPos = pos; repaint(); } }
+    void setFramePosition (float pos) { if (changed (wtPos, pos)) { wtPos = pos; repaint(); } }
     void setEnabled (bool e) { if (enabled != e) { enabled = e; repaint(); } }
 
     void paint (juce::Graphics& g) override;