Duplicated gRPC-response-to-ResponseDirectMessage mapping

The conversion from a gRPC message proto to `ResponseDirectMessage` appears identically in both `handle_get_paginated_messages` (lines 226-237) and `handle_sync_messages` (lines 438-449). Same field-by-field map with the same `Uuid::parse_str(...).unwrap_or_else(|_| Uuid::new_v4())` fallback.

hint: Implement `From` for `ResponseDirectMessage` (or a named conversion function). Both call sites collapse to `.map(ResponseDirectMessage::from)`.

Find the implementations of handle_get_paginated_messages and handle_sync_messages, then compare their duplicated ProtoMessage-to-ResponseDirectMessage mappings. Inspect the ProtoMessage and ResponseDirectMessage definitions before choosing the conversion approach. Done means both handlers use the shared conversion and existing Rust tests still pass.

Written by the indexing model from the issue text.