Parametric bracket as OpenSCAD-style code in JavaScript

Build a single-file Three.js page that constructs a printable L-bracket from parameters using constructive solid geometry you implement or compose from BufferGeometries (no CSG library). Parameters exposed as range inputs: width, height, depth, thickness, hole diameter, hole count per leg. The bracket must update live as sliders move. Show a wireframe toggle and a dimension readout. Add an "Export STL" button that generates ASCII STL from the current mesh (write the exporter yourself) and downloads it. Expose window.__xobench.setCamera(angleDeg) and window.__xobench.getSTL() returning the STL string. Return the complete file in one code block.