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/entrypoint.sh

@@ -1,7 +1,7 @@
 #!/bin/bash
 set -euo pipefail
 
-DATA_DIR="/app/data"
+export DATA_DIR="/app/data"
 
 # Create symlinks so scripts (which write to /app/) persist data to the volume
 for f in byty_sreality.json byty_realingo.json byty_bezrealitky.json \
@@ -18,8 +18,5 @@ crond -b -l 2
 echo "[entrypoint] Starting initial scrape in background..."
 bash /app/run_all.sh &
 
-echo "[entrypoint] Starting ratings API server on port 8081..."
-DATA_DIR="$DATA_DIR" python3 /app/ratings_server.py &
-
-echo "[entrypoint] Starting HTTP server on port 8080..."
-exec python3 -m http.server 8080 --directory "$DATA_DIR"
+echo "[entrypoint] Starting server on port 8080..."
+exec python3 /app/server.py