Add status dashboard, server, scraper stats, and DATA_DIR support

Key changes:
- Replace ratings_server.py + status.html with a unified server.py that
  serves the map, scraper status dashboard, and ratings API in one process
- Add scraper_stats.py utility: each scraper writes per-run stats (fetched,
  accepted, excluded, duration) to stats_<source>.json for the status page
- generate_status.py: respect DATA_DIR env var so status.json lands in the
  configured data directory instead of always the project root
- run_all.sh: replace the {"status":"running"} overwrite of status.json with
  a dedicated scraper_running.json lock file; trap on EXIT ensures cleanup
  even on kill/error, preventing the previous run's results from being wiped
- server.py: detect running state via scraper_running.json existence instead
  of status["status"] field, eliminating the dual-use race condition
- Makefile: add serve (local dev), debug (Docker debug container) targets;
  add SERVER_PORT variable
- build/Dockerfile + entrypoint.sh: switch to server.py, set DATA_DIR,
  adjust volume mounts
- .gitignore: add *.json and *.log to keep runtime data files out of VCS
- mapa_bytu.html: price-per-m² colouring, status link, UX tweaks

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

build/Dockerfile

@@ -10,7 +10,8 @@ WORKDIR /app
 
 COPY scrape_and_map.py scrape_realingo.py scrape_bezrealitky.py \
      scrape_idnes.py scrape_psn.py scrape_cityhome.py \
-     merge_and_map.py regen_map.py run_all.sh ratings_server.py ./
+     merge_and_map.py regen_map.py generate_status.py scraper_stats.py \
+     run_all.sh server.py ./
 
 COPY build/crontab /etc/crontabs/root
 COPY build/entrypoint.sh /entrypoint.sh
@@ -18,7 +19,7 @@ RUN chmod +x /entrypoint.sh run_all.sh
 
 RUN mkdir -p /app/data
 
-EXPOSE 8080 8081
+EXPOSE 8080
 
 HEALTHCHECK --interval=60s --timeout=5s --start-period=300s \
     CMD wget -q -O /dev/null http://localhost:8080/ || exit 1