Apply rule_templates to a raw JSON message

Apply a set of rule_template records to a raw JSON payload. The ``rules`` list contains rule_template records fetched from the external API. This service does not store them — it only executes them. Only ``is_active=true`` rules are applied, sorted by ``position`` ascending. Rules with ``condition_data`` are skipped when their condition is not met. ``CUSTOM_JS`` rules run a sandboxed JavaScript snippet over the payload (unless disabled via settings, in which case they are reported as errored). Returns the original payload, the transformed payload, and a per-rule log. When ``include_diff=true``, a ``diff`` field carries the before/after state of the payload around each rule, for the UI to debug modifications.