feat(db): block deleting an org that still has service users

internal/store/postgres/migrations/20260723120000_restrict_org_delete_with_serviceusers.down.sql

@@ -0,0 +1,2 @@
+DROP TRIGGER IF EXISTS trg_serviceusers_block_org_delete ON organizations;
+DROP FUNCTION IF EXISTS serviceusers_block_org_delete();

internal/store/postgres/migrations/20260723120000_restrict_org_delete_with_serviceusers.up.sql

@@ -0,0 +1,26 @@
+-- Block deleting an organization that still has service users.
+
+-- A plain foreign key to organizations(id) cannot be used here. The bootstrap
+-- superuser lives under the virtual platform org (00000000-0000-0000-0000-000000000000),
+-- which has no row in organizations by design. A BEFORE DELETE trigger only
+-- fires when a real org is deleted, so the virtual platform org and its
+-- bootstrap service account are never in scope.
+--
+-- Existing orphaned rows (if any) are left untouched; they are cleaned up out
+-- of band, not by this migration.
+CREATE OR REPLACE FUNCTION serviceusers_block_org_delete()
+    RETURNS trigger AS $$
+BEGIN
+    IF EXISTS (SELECT 1 FROM serviceusers WHERE org_id = OLD.id) THEN
+        RAISE EXCEPTION 'cannot delete organization %: service users still reference it', OLD.id
+            USING ERRCODE = 'foreign_key_violation';
+    END IF;
+    RETURN OLD;
+END;
+$$ LANGUAGE plpgsql;
+
+DROP TRIGGER IF EXISTS trg_serviceusers_block_org_delete ON organizations;
+CREATE TRIGGER trg_serviceusers_block_org_delete
+    BEFORE DELETE ON organizations
+    FOR EACH ROW
+    EXECUTE FUNCTION serviceusers_block_org_delete();