Add Docker setup with multi-stage build and Compose deploy config

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Dockerfile

@@ -0,0 +1,35 @@
+# ── Stage 1: Dependencies (mit Compiler für better-sqlite3) ──────────────────
+FROM node:20.19.2-slim AS deps
+
+WORKDIR /app
+
+RUN apt-get update && apt-get install -y --no-install-recommends \
+        python3 make g++ \
+    && rm -rf /var/lib/apt/lists/*
+
+COPY package.json package-lock.json ./
+RUN npm ci --omit=dev
+
+# ── Stage 2: Runtime ──────────────────────────────────────────────────────────
+FROM node:20.19.2-slim AS runtime
+
+WORKDIR /app
+
+RUN groupadd --system --gid 1001 nodejs \
+    && useradd --system --uid 1001 --gid nodejs --no-create-home appuser
+
+COPY --from=deps /app/node_modules ./node_modules
+COPY . .
+
+RUN mkdir -p data && chown -R appuser:nodejs data
+
+VOLUME ["/app/data"]
+
+USER appuser
+
+EXPOSE 3000
+
+HEALTHCHECK --interval=30s --timeout=5s --start-period=10s --retries=3 \
+    CMD node -e "require('http').get('http://localhost:3000/',r=>process.exit(r.statusCode===200?0:1)).on('error',()=>process.exit(1))"
+
+CMD ["node", "server.js"]