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/FilterBank.cpp

@@ -1,14 +1,15 @@
 #include "FilterBank.h"
+#include "ExactCompare.h"
 
 namespace serum
 {
 
-void FilterBank::prepare (double sampleRate, int maxBlockSize)
+void FilterBank::prepare (double sampleRate)
 {
-    f1L.prepare (sampleRate, maxBlockSize);
-    f1R.prepare (sampleRate, maxBlockSize);
-    f2L.prepare (sampleRate, maxBlockSize);
-    f2R.prepare (sampleRate, maxBlockSize);
+    f1L.prepare (sampleRate);
+    f1R.prepare (sampleRate);
+    f2L.prepare (sampleRate);
+    f2R.prepare (sampleRate);
 }
 
 void FilterBank::reset()
@@ -67,8 +68,9 @@ void FilterBank::process (float* l, float* r, int numSamples, const FilterBankPa
         applySlot (f2R, r, numSamples, p.f2On, p.f2Type, p.f2Cutoff, p.f2Res, p.f2Drive, p.f2Key, p.f2Slope, noteHz);
     }
 
-    // Post-filter output level.
-    if (p.out != 1.0f)
+    // Post-filter output level. Skip the multiply only at exact unity so the
+    // bypass never changes the rendered samples.
+    if (! exactly (p.out, 1.0f))
     {
         for (int i = 0; i < numSamples; ++i)
         {