chore: consolidate to single Docker container

Replace two-container setup (separate backend + nginx frontend) with a
single image that runs both via supervisord:

- New Dockerfile: Node stage builds React, Python+nginx stage is the runtime
- supervisord.conf: manages uvicorn (api_server.py) + nginx as sibling procs
- nginx.conf: proxy_pass updated to localhost:8000 (same container)
- docker-compose.yml: simplified to one service on port 80

Deploy:
  docker-compose up -d        # or
  docker build -t flight-radar . && docker run -p 80:80 flight-radar

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

flight-comparator/Dockerfile

@@ -0,0 +1,54 @@
+# ── Stage 1: Build React frontend ─────────────────────────────────────────
+FROM node:20-alpine AS frontend-builder
+
+WORKDIR /app
+COPY frontend/package*.json ./
+RUN npm ci
+COPY frontend/ .
+RUN npm run build
+
+# ── Stage 2: Single runtime image ─────────────────────────────────────────
+FROM python:3.11-slim
+
+ENV PYTHONUNBUFFERED=1 \
+    PYTHONDONTWRITEBYTECODE=1 \
+    PIP_NO_CACHE_DIR=1
+
+# Install nginx, supervisor, and gcc (for some pip packages)
+RUN apt-get update && apt-get install -y --no-install-recommends \
+    nginx \
+    supervisor \
+    gcc \
+    && rm -rf /var/lib/apt/lists/*
+
+WORKDIR /app
+
+# Python dependencies
+COPY requirements.txt .
+RUN pip install --no-cache-dir -r requirements.txt
+
+# Backend source
+COPY api_server.py airports.py cache.py ./
+COPY database/ ./database/
+
+# Frontend build output
+COPY --from=frontend-builder /app/dist /usr/share/nginx/html
+
+# Config files
+COPY nginx.conf /etc/nginx/conf.d/default.conf
+COPY supervisord.conf /etc/supervisor/conf.d/app.conf
+
+# Remove the default nginx site
+RUN rm -f /etc/nginx/sites-enabled/default
+
+# Pre-fetch airport data and initialise the database at build time
+RUN mkdir -p data && \
+    python -c "from airports import download_and_build_airport_data; download_and_build_airport_data()" && \
+    python database/init_db.py
+
+EXPOSE 80
+
+HEALTHCHECK --interval=30s --timeout=5s --start-period=15s --retries=3 \
+    CMD wget -q --spider http://localhost/ || exit 1
+
+CMD ["/usr/bin/supervisord", "-n", "-c", "/etc/supervisor/conf.d/app.conf"]