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.frontend

@@ -1,36 +0,0 @@
-# Frontend Dockerfile for Flight Radar UI
-# Stage 1: Build React application
-FROM node:20-alpine AS builder
-
-WORKDIR /app
-
-# Copy package files
-COPY frontend/package*.json ./
-
-# Install dependencies
-RUN npm ci
-
-# Copy source code
-COPY frontend/ .
-
-# Build production app
-RUN npm run build
-
-# Stage 2: Serve with nginx
-FROM nginx:alpine
-
-# Copy built assets from builder stage
-COPY --from=builder /app/dist /usr/share/nginx/html
-
-# Copy nginx configuration
-COPY nginx.conf /etc/nginx/conf.d/default.conf
-
-# Expose port
-EXPOSE 80
-
-# Health check
-HEALTHCHECK --interval=30s --timeout=3s --start-period=5s --retries=3 \
-    CMD wget --quiet --tries=1 --spider http://localhost/ || exit 1
-
-# Start nginx
-CMD ["nginx", "-g", "daemon off;"]