feat: dockerfiles and full docker-compose orchestration

Add multi-stage Dockerfiles for Python services (Dockerfile.service) and
React dashboard (Dockerfile.dashboard + nginx.conf). Update docker-compose.yml
with all seven application services: news-fetcher, sentiment-analyzer,
signal-generator, trade-executor, learning-engine, api-gateway, and dashboard.

docker/Dockerfile.dashboard

@@ -0,0 +1,34 @@
+# Multi-stage Dockerfile for the React dashboard.
+# Stage 1: build the Vite/React app
+# Stage 2: serve via nginx
+
+# ---------------------------------------------------------------------------
+# Stage 1: Node build
+# ---------------------------------------------------------------------------
+FROM node:20-alpine AS builder
+
+WORKDIR /app
+
+COPY dashboard/package.json dashboard/package-lock.json ./
+RUN npm ci
+
+COPY dashboard/ .
+RUN npm run build
+
+# ---------------------------------------------------------------------------
+# Stage 2: nginx to serve the static build
+# ---------------------------------------------------------------------------
+FROM nginx:alpine
+
+# Remove default nginx site
+RUN rm /etc/nginx/conf.d/default.conf
+
+# Copy custom nginx config
+COPY docker/nginx.conf /etc/nginx/conf.d/default.conf
+
+# Copy built assets from the builder stage
+COPY --from=builder /app/dist /usr/share/nginx/html
+
+EXPOSE 80
+
+CMD ["nginx", "-g", "daemon off;"]