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/supervisord.conf

@@ -0,0 +1,24 @@
+[supervisord]
+nodaemon=true
+logfile=/dev/null
+logfile_maxbytes=0
+pidfile=/tmp/supervisord.pid
+
+[program:api]
+command=python /app/api_server.py
+directory=/app
+autostart=true
+autorestart=true
+stdout_logfile=/dev/stdout
+stdout_logfile_maxbytes=0
+stderr_logfile=/dev/stderr
+stderr_logfile_maxbytes=0
+
+[program:nginx]
+command=nginx -g "daemon off;"
+autostart=true
+autorestart=true
+stdout_logfile=/dev/stdout
+stdout_logfile_maxbytes=0
+stderr_logfile=/dev/stderr
+stderr_logfile_maxbytes=0