v3: Dockerfile — fetch pinned OpenCV.js WASM at build time

Dockerfile

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+FROM node:20-alpine
+WORKDIR /app
+COPY package.json ./
+RUN npm install --omit=dev
+# OpenCV.js WASM for the v3 board-solve engine — fetched at build time so the
+# repo stays small. Pinned to the build validated against the solver tests.
+RUN npm install --no-save @techstark/opencv-js@4.12.0-release.1 \
+ && mkdir -p public/vendor \
+ && cp node_modules/@techstark/opencv-js/dist/opencv.js public/vendor/opencv.js \
+ && rm -rf node_modules/@techstark
+COPY server ./server
+COPY data ./data
+COPY public ./public
+ENV PORT=33044
+ENV LIVE_DIR=/app/data/live
+EXPOSE 33044
+CMD ["node", "server/server.js"]