feat: drag files between file panes (move or copy, SSH hosts too) and into a terminal of the same machine

internal/proto/proto.go

@@ -366,6 +366,9 @@ type FSShipArgs struct {
 	Chunk    int        `json:"chunk,omitempty"`
 	Job      string     `json:"job,omitempty"`
 	SSH      *SSHTarget `json:"ssh,omitempty"`
+	// Conn: the files of this side are on the SSH host of this agent's file
+	// connection (an SSH file pane), not on the machine itself.
+	Conn string `json:"conn,omitempty"`
 }
 
 // ShipProgress is what a sending machine reports: bytes of files sent out of