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/Engine.h

@@ -25,6 +25,12 @@ public:
     void prepare (double sampleRate, int blockSize, juce::AudioProcessorValueTreeState& apvts);
     void reset();
 
+    // Ask for the DSP state to be cleared before the next block is rendered.
+    // Safe to call from the message thread while controlLock is held: the audio
+    // thread performs the reset in captureControls, so the DSP objects are only
+    // ever touched by the audio thread.
+    void requestReset() noexcept;
+
     void processBlock (juce::AudioBuffer<float>& buffer,
                        juce::MidiBuffer& midi,
                        juce::AudioProcessorValueTreeState& apvts,
@@ -43,8 +49,6 @@ public:
     const WavetableLibrary& getWavetables() const { return wavetables; }
     void setLfoShapeData (int index, const std::vector<float>& data, int steps);
 
-    int getActiveVoiceCount() const { return activeVoiceCount.load (std::memory_order_relaxed); }
-
 private:
     std::array<SynthVoice, kNumVoices> voices;
     std::array<LFO, kNumLfos> lfos, controlLfos;
@@ -53,6 +57,7 @@ private:
     ModulationMatrix matrix, audioMatrix;
     MacroControls macros, audioMacros;
     juce::CriticalSection controlLock;
+    bool resetRequested = false;   // guarded by controlLock
 
     struct ParameterValue
     {
@@ -67,7 +72,6 @@ private:
     float  pitchBend = 0.0f;
     float  modWheel  = 0.0f;
     juce::uint64 noteCounter = 0;
-    std::atomic<int> activeVoiceCount { 0 };
 
     juce::AudioBuffer<float> mixBuffer;