Add web host: wasm bridge, page shell, pixel GAME OVER, Playwright smoke tests

web/build.sh

@@ -0,0 +1,13 @@
+#!/bin/sh
+# Builds web/dist: the gallery as wasm plus the page shell.
+set -eu
+cd "$(dirname "$0")/.."
+build=$(git rev-parse --short HEAD)-$(date +%s)
+rm -rf web/dist
+mkdir -p web/dist
+GOOS=js GOARCH=wasm go build -trimpath -ldflags="-s -w" -o web/dist/app.wasm ./cmd/web
+cp "$(go env GOROOT)/lib/wasm/wasm_exec.js" web/dist/
+for f in index.html main.js; do
+  sed "s/__BUILD__/$build/g" "web/$f" > "web/dist/$f"
+done
+echo "web/dist built: $build, app.wasm $(wc -c < web/dist/app.wasm) bytes"