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.backend

@@ -1,47 +0,0 @@
-# Backend Dockerfile for Flight Radar API
-FROM python:3.11-slim
-
-# Set working directory
-WORKDIR /app
-
-# Set environment variables
-ENV PYTHONUNBUFFERED=1 \
-    PYTHONDONTWRITEBYTECODE=1 \
-    PIP_NO_CACHE_DIR=1 \
-    PIP_DISABLE_PIP_VERSION_CHECK=1
-
-# Install system dependencies
-RUN apt-get update && apt-get install -y \
-    gcc \
-    && rm -rf /var/lib/apt/lists/*
-
-# Copy requirements file
-COPY requirements.txt .
-
-# Install Python dependencies
-RUN pip install --no-cache-dir -r requirements.txt
-
-# Copy application code
-COPY api_server.py .
-COPY airports.py .
-COPY cache.py .
-COPY database/ ./database/
-
-# Create necessary directories
-RUN mkdir -p data
-
-# Download airport data on build
-RUN python -c "from airports import download_and_build_airport_data; download_and_build_airport_data()"
-
-# Initialize database
-RUN python database/init_db.py
-
-# Expose port
-EXPOSE 8000
-
-# Health check
-HEALTHCHECK --interval=30s --timeout=3s --start-period=5s --retries=3 \
-    CMD python -c "import requests; requests.get('http://localhost:8000/health').raise_for_status()"
-
-# Run the application
-CMD ["python", "api_server.py"]