feat(#1685): surface attachments in read_room + add download_file

hive-matrix-mcp/src/protocol.rs

@@ -86,6 +86,17 @@ pub enum DaemonRequest {
     #[serde(rename = "read_room")]
     ReadRoom { room: String, limit: Option<usize> },
 
+    /// Download the media attachment carried by `event_id` in `room`
+    /// and write it to a local file (`dest_path`, or a temp file named
+    /// after the attachment when omitted), returning the path. The
+    /// read-side counterpart of `send_file`.
+    #[serde(rename = "download_file")]
+    DownloadFile {
+        room: String,
+        event_id: String,
+        dest_path: Option<String>,
+    },
+
     /// List rooms this agent has been invited to but not yet joined.
     /// Returns each room's id, canonical alias (when present), and
     /// display name.