test(3d): screenshot-baseline TDD suite for the 3D viewer OpenGL->WebGL port — 47 native goldens + red-state WebGL harness

tests/3d-regression mirrors the gal-regression pattern at renderer scale:
shared C++ scenarios call real KiCad 3D-viewer code (opengl_utils, display
lists + DrawCulled stencil subtraction, MODEL_3D VBOs, private generators via
a rob-template accessor, and full reload()+Redraw() composites over a
synthetic BOARD_ADAPTER). A native macOS harness renders them on real OpenGL
into 47 committed goldens (bit-deterministic, FBO capture); the wasm harness
compiles the same TUs against wasm/stubs/gl_ffp_stub.c no-ops so every
scenario renders blank — the TDD red state (parity meter: 47/47 changed).
Comparisons use the CI pixelmatch engine via the new generic compare-dirs.ts
(floors.json levels; manifest.json cmp-guards registry drift).

Documents an upstream bug: appendPostMachiningGeometry's countersink path
adds middle quads without normals, silently erasing the walls of any
display list it is batched into (3d-post-machining.png keeps the lists
separate to record it).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

tests/apps/3d-webgl/3d_webgl_test.html

@@ -0,0 +1,35 @@
+<!DOCTYPE html>
+<html lang="en">
+<head>
+  <meta charset="utf-8">
+  <title>3D Renderer WebGL Test</title>
+  <style>
+    body { margin: 0; background: #202020; }
+    #canvas { display: block; width: 800px; height: 600px; }
+  </style>
+</head>
+<body>
+  <canvas id="canvas" width="800" height="600"></canvas>
+  <script>
+    let ready = false;
+    let wasmModule = null;
+
+    window._threeDTestReady = () => { ready = true; };
+
+    window.threeDTest = {
+      isReady: () => ready,
+      runScenario: (i) => wasmModule.ccall('runScenario', 'number', ['number'], [i]),
+      getTotalScenarios: () => wasmModule.ccall('getTotalScenarios', 'number', [], []),
+      getScenarioName: (i) => wasmModule.ccall('getScenarioName', 'string', ['number'], [i]),
+      getCanvasWidth: () => wasmModule.ccall('getCanvasWidth', 'number', [], []),
+      getCanvasHeight: () => wasmModule.ccall('getCanvasHeight', 'number', [], []),
+    };
+  </script>
+  <script src="3d_webgl_test.js"></script>
+  <script>
+    create3DTest({ canvas: document.getElementById('canvas') })
+      .then((mod) => { wasmModule = mod; })
+      .catch((err) => { console.error('[3d-webgl] module init failed:', err); });
+  </script>
+</body>
+</html>