Four frames for the chair spectator and the turned CPU

The last two bodies still shuffling on two frames. Both get their in-between
strides, generated against their own art and fitted per channel onto it.

The chair-down stagger was walk frame 3, which a four-frame cycle would have
walked straight through — it is its own sprite now (z_sdown), picked by state
rather than by where the cycle happens to be.

Also fixed a strobe that predates all of this: z_c2's racket was drawn BLUE
while every other frame of the same zombie carries a brown one, so it flashed
once per cycle. Remapped onto z_c1's racket palette.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

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