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>

scripts/build-3d-native-test.sh

@@ -0,0 +1,55 @@
+#!/bin/bash
+#
+# Build script for the native 3D-renderer test harness (tests/3d-regression/native).
+#
+# Builds a standalone macOS application that renders the shared 3D scenarios
+# through KiCad's actual RENDER_3D_OPENGL code paths (real desktop OpenGL) and
+# writes golden baseline PNGs for the OpenGL->WebGL port regression suite.
+#
+# Modeled on scripts/build-gal-native-test.sh.
+#
+
+set -e
+
+SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+PROJECT_ROOT="$(cd "$SCRIPT_DIR/.." && pwd)"
+TEST_DIR="$PROJECT_ROOT/tests/3d-regression/native"
+BUILD_DIR="$TEST_DIR/build"
+LOG_FILE="$PROJECT_ROOT/tests/logs/3d-native-build.log"
+
+mkdir -p "$(dirname "$LOG_FILE")"
+
+echo "Building 3D Renderer Native Test..."
+echo "  Test dir: $TEST_DIR"
+echo "  Build dir: $BUILD_DIR"
+echo "  Log file: $LOG_FILE"
+
+mkdir -p "$BUILD_DIR"
+
+echo "Running CMake..."
+if ! cmake -S "$TEST_DIR" -B "$BUILD_DIR" >> "$LOG_FILE" 2>&1; then
+    echo "CMake configuration failed! Check $LOG_FILE for details."
+    echo ""
+    echo "Last 50 lines of log:"
+    tail -50 "$LOG_FILE"
+    exit 1
+fi
+
+echo "Building..."
+if ! make -C "$BUILD_DIR" -j"$(sysctl -n hw.ncpu 2>/dev/null || echo 4)" >> "$LOG_FILE" 2>&1; then
+    echo "Build failed! Check $LOG_FILE for details."
+    echo ""
+    echo "Last 100 lines of log:"
+    tail -100 "$LOG_FILE"
+    exit 1
+fi
+
+echo "Build successful!"
+echo "Executable: $BUILD_DIR/scene3d_native_test"
+echo ""
+echo "Options:"
+echo "  --output <dir>    Output directory for 3d-<name>.png"
+echo "  --manifest <file> Write the scenario manifest JSON"
+echo "  --filter <substr> Only run scenarios whose name contains <substr>"
+echo "  --list            Print scenario names and exit"
+echo "  --show            Keep the window open after rendering"