List HTTP action diagnostics

Requires actions:http:diagnostics:read. Existing HTTP diagnostics, distinct from unified /action-executions history. Optional actionId must have http: prefix. Uses existing bounded HTTP-log cursor semantics. This route retains the legacy diagnostic format and stored payloads for compatibility; it does not apply the newer inspection snapshot bounds/redaction. For bounded redacted saved requests and responses, prefer get_action_execution with includeInspection=true and explicit action_inspection:read. Neither route executes the action.