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/Presets/AGENTS.md

@@ -0,0 +1,33 @@
+# presets module
+
+## Owned files
+
+- FactoryPresets.h
+- FactoryPresets.cpp
+
+## Rules
+
+- Build presets as sparse maps; unset parameters keep their APVTS defaults.
+- Use `ids::` for every parameter ID, never raw strings.
+- Use named helpers (coarse, unison, slope, fx, lfoShape, mod) to build normalized values.
+- Return the preset list as `const std::vector<FactoryPreset>&` from a static local.
+- Reference `ModConnection` and macro assignment structs instead of ad hoc tuples.
+
+## IF-THEN
+
+- IF a preset omits a parameter THEN leave it at its default; do not write an explicit zero.
+- IF a preset sets a physical value THEN encode it through the same `maps::` helpers the DSP uses.
+
+## Examples
+
+```cpp
+// BAD: raw string ID and an opaque normalized number
+pr.params = { { "oscAUnison", 0.4f } };
+```
+
+```cpp
+// GOOD: ids:: and a named helper
+pr.params = { p (ids::oscAUnison, unison (7)) };
+```
+
+This file overrides /AGENTS.md where they conflict.