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.service

@@ -0,0 +1,45 @@
+# Multi-stage Dockerfile for all Python microservices.
+# Build args:
+#   EXTRAS  — pip optional-dependency groups (e.g. "news", "sentiment,trading")
+#   SERVICE_MODULE — Python module name under services/ (e.g. "news_fetcher")
+
+# ---------------------------------------------------------------------------
+# Stage 1: builder — install Python dependencies
+# ---------------------------------------------------------------------------
+FROM python:3.12-slim AS builder
+
+WORKDIR /app
+
+# Copy project metadata and source so pip can resolve the local package
+COPY pyproject.toml .
+COPY shared/ shared/
+COPY services/ services/
+COPY backtester/ backtester/
+COPY alembic/ alembic/
+COPY alembic.ini .
+
+ARG EXTRAS="dev"
+RUN pip install --no-cache-dir ".[$EXTRAS]"
+
+# ---------------------------------------------------------------------------
+# Stage 2: slim runtime image
+# ---------------------------------------------------------------------------
+FROM python:3.12-slim
+
+WORKDIR /app
+
+# Copy installed packages and CLI entry-points from the builder
+COPY --from=builder /usr/local/lib/python3.12/site-packages /usr/local/lib/python3.12/site-packages
+COPY --from=builder /usr/local/bin /usr/local/bin
+
+# Copy application source code
+COPY --from=builder /app .
+
+ARG SERVICE_MODULE="api_gateway"
+ENV SERVICE_MODULE=${SERVICE_MODULE}
+
+# Simple health check — verify the Python process is running
+HEALTHCHECK --interval=30s --timeout=10s --start-period=15s --retries=3 \
+    CMD python -c "import sys; sys.exit(0)" || exit 1
+
+CMD python -m services.${SERVICE_MODULE}.main