`TenantConfigManager.update_single_config` has no `value` argument — it can only bump timestamps

[taoh88]

backend/utils/config_utils.py:150-165:

def update_single_config(self, tenant_id: str | None = None, key: str | None = None):
    """Update configuration value in database"""
    if tenant_id is None:
        logger.warning(...)
        return

    existing_config = get_single_config_info(tenant_id, key)
    if existing_config:
        update_data = {
            "updated_by": tenant_id,
            "update_time": func.current_timestamp()
        }
        update_config_by_tenant_config_id_and_data(
            existing_config["tenant_config_id"], update_data)
        return

The signature accepts tenant_id and key but no value. The function looks up the existing row and writes back only updated_by + update_time. The actual config_value column is untouched. Calling this method to "update" a config in fact does nothing observable from the API surface — just touches the audit metadata.

Compare with set_single_config directly above (lines 115-135) which does the same key plus a real config_value. That's the body the update method appears to want.

Either:

1. The intended signature should include value, and the body should pass "config_value": value into update_data — in which case this is dead/broken code with a misleading name; or
2. The method is genuinely meant to be a "touch" / re-stamp helper and should be renamed touch_single_config to make the contract honest.

A grep of the codebase reveals no caller using update_single_config, suggesting nobody noticed because nobody invokes it — which is its own smell.

Severity: Low (no user-visible breakage today), but high confusion risk for the next contributor.