The ornamental design for a headboard, as shown and described.
FIG. 1 is a perspective view of a headboard showing my new design; the
opposite side being a mirror image thereof; and,
FIG. 2 is a front elevational view.
The broken line showing of the bottom edge of the headboard defines the
boundary but forms no part of the claimed design. The broken line showing
of the two vertical supports is for environmental purposes only and forms
no part of the claimed design.