When switching from C15 to Additive or FM engines, the MLP was resized
to 0 outputs because paramMeta wasn't loaded until init() (which needs
AudioContext). The SynthVisualizer also disappeared because its section
map was hardcoded to C15's 18 param groups.
- Add FaustEngineBase.loadParamMeta() for eager JSON-only loading
- Call loadParamMeta() before setActiveEngine() in engine switch handler
- Add SynthVisualizer.rebuild(paramMeta) to derive sections from groups
- Add rebuildParamToSection() / restoreC15ParamToSection() for engine-agnostic
param-to-section mapping
- Fix tooltip to use engineParamOverrides for non-C15 engines
f19d5e5baa