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/MacroControls.cpp

@@ -1,4 +1,5 @@
 #include "MacroControls.h"
+#include "ExactCompare.h"
 
 namespace serum
 {
@@ -79,7 +80,7 @@ void MacroControls::fromValueTree (const juce::ValueTree& tree)
             continue;
         const double savedIndex = (double) mac.getProperty ("index", -1);
         if (! std::isfinite (savedIndex) || savedIndex < 0.0 || savedIndex >= kNumMacros
-            || std::floor (savedIndex) != savedIndex)
+            || ! isWholeNumber (savedIndex))
             continue;
         const int index = (int) savedIndex;
         for (const auto& asg : mac)