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/modulation/AGENTS.md

@@ -0,0 +1,34 @@
+# modulation module
+
+## Related source files
+
+This directory contains guidance; implementations remain in the parent `Source/`
+directory:
+
+- `../ModulationMatrix.h`, `../ModulationMatrix.cpp`
+- `../MacroControls.h`, `../MacroControls.cpp`
+- `../RAVEButton.h`, `../RAVEButton.cpp`, which define `RaveController`
+
+## Rules
+
+- Use `bool` return codes for bounded inserts (`addConnection`, `addAssignment`).
+- Require a cap on connection and assignment counts (`kMaxConnections`, `kMaxAssignments`).
+- Serialise and restore state through `juce::ValueTree` so presets survive save and load.
+- Never accept a `ModTarget::None` connection; reject it and return false.
+- RaveController applies a non-destructive boost to render settings. It does not write APVTS parameters or keep a restoration snapshot.
+- Keep the existing RAVEButton filenames unless a rename is explicitly in scope.
+
+## GUI/audio state
+
+Hold `Engine::getControlLock()` while reading or editing the control-side matrix,
+macro assignments, or LFO shapes. The audio thread tries that lock once per block
+and copies into reserved audio-side storage. If the lock is busy, it keeps the
+previous settings and continues rendering. Never iterate the control-side vectors
+from the render path.
+
+Master and FX-mix modulation use global sources directly. Per-voice sources for
+those destinations come from the newest active voice.
+
+If `addConnection` or `addAssignment` returns false, handle the failed insert.
+
+This file refines the repository-root AGENTS.md for the related sources.