Fix GeoIP download (HTTP 403) and clarify host setup

- db-ip.com rejects Python's default "Python-urllib" user agent with
  403; the download now sends "fail2ban-webui/<version> (+repo URL)"
- README quick start: edit .env and replace the example hosts in
  config/hosts.yaml; hosts.yaml.example marks its entries as examples

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

examples/hosts.yaml.example

@@ -8,6 +8,8 @@
 #
 # After changes: docker compose run --rm -it fail2ban-webui keyscan
 #                docker compose restart
+#
+# The three entries below are EXAMPLES – replace them with your own hosts.
 # =====================================================================
 hosts:
   - name: web01