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/services/oidc_token_service.py

@@ -324,8 +324,8 @@ class OIDCTokenService:
             List of role objects with organization_id and role
         """
         roles = []
-        if user and user.organization_memberships:
-            for member in user.organization_memberships:
+        if user:
+            for member in user.get_active_memberships():
                 roles.append({
                     "organization_id": str(member.organization_id),
                     "role": member.role.value