Refactor ban management with domain models and mappers

- Add ban domain model for core business logic separation
- Implement mapper pattern for DTO/domain conversions
- Update ban service with new domain-driven approach
- Refactor router endpoints to use new architecture
- Add comprehensive mapper tests
- Update documentation with architecture changes

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

backend/app/mappers/__init__.py

@@ -0,0 +1,27 @@
+"""Response mappers.
+
+Convert domain models (from services) to response models (for HTTP API).
+
+This is the mapping layer at the router boundary, ensuring the service layer
+remains independent of HTTP response shapes.
+"""
+
+from app.mappers.ban_mappers import (
+    map_domain_active_ban_list_to_response,
+    map_domain_active_ban_to_response,
+    map_domain_ban_trend_to_response,
+    map_domain_bans_by_country_to_response,
+    map_domain_bans_by_jail_to_response,
+    map_domain_dashboard_ban_item_to_response,
+    map_domain_dashboard_ban_list_to_response,
+)
+
+__all__ = [
+    "map_domain_active_ban_to_response",
+    "map_domain_active_ban_list_to_response",
+    "map_domain_dashboard_ban_item_to_response",
+    "map_domain_dashboard_ban_list_to_response",
+    "map_domain_bans_by_country_to_response",
+    "map_domain_ban_trend_to_response",
+    "map_domain_bans_by_jail_to_response",
+]