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/PluginEditor.h

@@ -2,7 +2,6 @@
 
 #include <JuceHeader.h>
 #include "PluginProcessor.h"
-#include "GUI/SerumLookAndFeel.h"
 #include "GUI/Knob.h"
 #include "GUI/Slider.h"
 #include "GUI/ToggleButton.h"
@@ -36,7 +35,6 @@ public:
 
 private:
     SerumAltAudioProcessor& processor;
-    SerumLookAndFeel laf;
 
     static constexpr int kBaseW = 1120;
     static constexpr int kBaseH = 740;
@@ -63,7 +61,6 @@ private:
     Panel oscAPanel { "Oscillator A" }, oscBPanel { "Oscillator B" };
     Panel subPanel { "Sub" }, noisePanel { "Noise" };
     WaveformDisplay oscAWave, oscBWave;
-    std::vector<juce::Component*> oscAComponents, oscBComponents;
 
     // --- FILTER ---
     Panel filter1Panel { "Filter 1" }, filter2Panel { "Filter 2" }, routingPanel { "Routing" };