The ornamental design for a seat, as shown and described.
FIG. 1 is a perspective view of a seat according to our design;
FIG. 2 is a front view of the seat of FIG. 1;
FIG. 3 is a rear view of the seat of FIG. 1;
FIG. 4 is a left side view of the seat of FIG. 1;
FIG. 5 is a right side view of the seat of FIG. 1; and,
FIG. 6 is a top view of the seat of FIG. 1.
The broken lines that are included in FIGS. 1-2 of the drawings denote aspects of the seat components that form no part of the claimed design. The bottom view is excluded, because it is plain and unornamented and, therefore, forms no part of the claimed design.