Scaffold vpinball-wasm: Emscripten port of Visual Pinball

Build scripts, CMake/source patches, npm packaging, and a Gitea CI
workflow to compile the real Visual Pinball engine (SDL3 + WebGL2 +
libwinevbs for real VBScript) to WebAssembly.

The patches are validated end-to-end: the patched engine boots in a
real browser, loads a real .vpx table, compiles its real GLSL shaders,
computes environment map radiance, initializes physics, and starts the
VBScript engine, before hanging on the one deliberately-deferred piece
of work (game loop rewrite around emscripten_set_main_loop), documented
in the README's roadmap.

scripts/clean.sh

@@ -0,0 +1,14 @@
+#!/usr/bin/env bash
+# Removes build artifacts. Pass --all to also remove the emsdk install
+# (slow to reinstall - kept by default across ordinary cleans).
+set -euo pipefail
+
+ROOT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")/.." && pwd)"
+
+rm -rf "$ROOT_DIR/vendor" "$ROOT_DIR/build" "$ROOT_DIR/dist"
+echo "Removed vendor/, build/, dist/"
+
+if [ "${1:-}" = "--all" ]; then
+   rm -rf "$ROOT_DIR/emsdk"
+   echo "Removed emsdk/"
+fi