fix(user): filter out soft-deleted memberships and organizations

Add get_active_memberships() method to User model that filters out
soft-deleted memberships and memberships of deleted organizations.
Update all usages of organization_memberships to use this method,
ensuring consistent handling of soft-deleted records across the
codebase. Also add deleted_at filters to CA queries in SSH helpers.

gatehouse_app/api/v1/users/admin.py

@@ -329,7 +329,7 @@ def admin_hard_delete_user(user_id):
     if target.id == caller.id:
         return api_response(success=False, message="Cannot delete your own account via this endpoint.", status=400, error_type="BAD_REQUEST")
 
-    target_org_ids = {m.organization_id for m in target.organization_memberships}
+    target_org_ids = {m.organization_id for m in target.get_active_memberships()}
     admin_in_shared_org = OrganizationMember.query.filter(
         OrganizationMember.user_id == caller.id,
         OrganizationMember.organization_id.in_(target_org_ids),