I claim the ornamental design for a headboard, as shown and described.
FIG. 1 is a front view of a headboard, showing my new design.
FIG. 2 is a right side view thereof.
FIG. 3 is a top view thereof.
FIG. 4 is a rear view thereof.
FIG. 5 is a bottom view thereof.
FIG. 6 is a front perspective view thereof; and,
FIG. 7 is a front perspective view thereof, shown within an environment of use.
The bed frame is shown in broken lines in the drawings to indicate that it forms no part of the claimed design for a headboard.
The headboard is shown with a symbolic break in its width. The appearance of any portion of the article between the break lines forms no part of the claimed design.