Add Docker deploy for Caddy production at cyd.smallzhiyuns.com.

Standalone Next image, local firmware sync volume, and docs for the existing host-network Caddy reverse proxy.

Co-authored-by: Cursor <cursoragent@cursor.com>

Dockerfile

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+# CYD Flasher — production image (Next.js standalone)
+FROM node:20-bookworm-slim AS deps
+WORKDIR /app
+COPY package.json package-lock.json ./
+RUN npm install
+
+FROM node:20-bookworm-slim AS builder
+WORKDIR /app
+COPY --from=deps /app/node_modules ./node_modules
+COPY . .
+RUN mkdir -p public
+ENV NEXT_TELEMETRY_DISABLED=1
+ARG NEXT_PUBLIC_SITE_URL=https://cyd.smallzhiyuns.com
+ENV NEXT_PUBLIC_SITE_URL=$NEXT_PUBLIC_SITE_URL
+RUN npm run build
+
+FROM node:20-bookworm-slim AS runner
+WORKDIR /app
+ENV NODE_ENV=production
+ENV NEXT_TELEMETRY_DISABLED=1
+ENV PORT=3000
+ENV HOSTNAME=0.0.0.0
+ENV NEXT_PUBLIC_SITE_URL=https://cyd.smallzhiyuns.com
+ENV CYD_FIRMWARE_ROOT=/app/firmware
+
+RUN addgroup --system --gid 1001 nodejs \
+  && adduser --system --uid 1001 nextjs
+
+COPY --from=builder /app/public ./public
+COPY --from=builder --chown=nextjs:nodejs /app/.next/standalone ./
+COPY --from=builder --chown=nextjs:nodejs /app/.next/static ./.next/static
+COPY --chown=nextjs:nodejs firmware ./firmware
+
+USER nextjs
+EXPOSE 3000
+CMD ["node", "server.js"]