feat: add Docker deployment — multi-stage build + nginx SPA serving

Dockerfile

@@ -0,0 +1,25 @@
+# ── Stage 1: Build ───────────────────────────────────────
+FROM node:22-alpine AS builder
+
+WORKDIR /app
+
+# Install dependencies first (layer cache)
+COPY package.json package-lock.json ./
+RUN npm ci
+
+# Copy source and build
+COPY . .
+RUN npm run build
+
+# ── Stage 2: Serve ───────────────────────────────────────
+FROM nginx:alpine AS runner
+
+# Copy built assets from builder
+COPY --from=builder /app/dist /usr/share/nginx/html
+
+# Copy custom nginx config for SPA routing
+COPY nginx.conf /etc/nginx/conf.d/default.conf
+
+EXPOSE 80
+
+CMD ["nginx", "-g", "daemon off;"]