feat(frontend): add React chat UI with SSE parsing and source accordion

frontend/Dockerfile

@@ -0,0 +1,23 @@
+FROM node:22-alpine AS build
+
+WORKDIR /app
+
+COPY package.json package-lock.json* ./
+RUN npm ci --no-audit --no-fund
+
+COPY tsconfig.json vite.config.ts index.html ./
+COPY src ./src
+
+RUN npm run build
+
+FROM nginx:1.27-alpine
+
+COPY nginx.conf /etc/nginx/conf.d/default.conf
+COPY --from=build /app/dist /usr/share/nginx/html
+
+EXPOSE 80
+
+HEALTHCHECK --interval=30s --timeout=5s --start-period=10s --retries=3 \
+    CMD wget -qO- http://localhost/ >/dev/null || exit 1
+
+CMD ["nginx", "-g", "daemon off;"]