feat: inject git SHA + build timestamp into version.json during docker build

Dockerfile

@@ -7,6 +7,15 @@ RUN cd client && npm install
 COPY client/ ./client/
 RUN cd client && npm run build
 
+# ── Version metadata ──────────────────────────────────────────────────────────
+# Pass these at build time:
+#   docker build --build-arg GIT_SHA=$(git rev-parse HEAD) \
+#                --build-arg BUILD_TIME=$(date -u +%Y-%m-%dT%H:%M:%SZ) .
+ARG GIT_SHA=dev
+ARG BUILD_TIME=unknown
+RUN echo "{\"sha\":\"${GIT_SHA}\",\"shortSha\":\"${GIT_SHA:0:7}\",\"buildTime\":\"${BUILD_TIME}\"}" \
+    > /build/client/dist/version.json
+
 FROM node:20-alpine AS production
 RUN apk add --no-cache chromium nss freetype harfbuzz ca-certificates ttf-freefont
 ENV PUPPETEER_SKIP_CHROMIUM_DOWNLOAD=true
@@ -25,5 +34,6 @@ COPY demo/        ./demo/
 COPY client/public/static ./client/dist/static
 RUN mkdir -p /data
 EXPOSE 3001
-HEALTHCHECK --interval=30s --timeout=5s --start-period=10s --retries=3   CMD wget -qO- http://localhost:3001/api/health || exit 1
+HEALTHCHECK --interval=30s --timeout=5s --start-period=10s --retries=3 \
+  CMD wget -qO- http://localhost:3001/api/health || exit 1
 CMD ["node", "server.js"]