Apply rule_templates to a raw HL7 message

Apply a set of rule_template records to a raw HL7 v2.x message. 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. Returns the original message, the transformed message, and a per-rule log. When ``include_diff=true``, a ``diff`` field carries the before/after state of the message around each rule, for the UI to debug modifications.