feat: update area management to implement hard delete and adjust related references

docs/DATABASE_SCHEMA.md

@@ -28,7 +28,7 @@ Schema truth is `migrations/*.sql`. This file is compact human map of current DB
 - `report_categories`
   citizen-facing report categories, `active`
 - `areas`
-  named municipal areas, GeoJSON polygon in `boundary_geojson`, `active`
+  named municipal areas, GeoJSON polygon in `boundary_geojson`
 - `team_categories`
   category of external intervention team
 - `teams`
@@ -92,7 +92,9 @@ Schema truth is `migrations/*.sql`. This file is compact human map of current DB
 - `reward_events(report_id, reason)` unique
 - `api_tokens.token_hash` unique
 - `intervention_access_links.token_hash` unique
-- category/team/area delete behavior is soft delete via `active = FALSE`
+- category/team delete behavior is soft delete via `active = FALSE`
+- area delete behavior is hard delete; linked `reports.area_id` and `teams.area_id`
+  become `NULL`
 
 ## Current Query Model
 - No generated ORM models