[vaprdev]

Summary

Creatures slid along with stiff legs, flipped when turning and varied in scale between scenes. A new src/creature.ts gives them jointed legs and real walk cycles.

+src/creature.ts
+  body(x, y, S, turn)      pose in body coordinates
+  stepGait(g, d/stride)    step cycle advances with distance walked, so feet don't slide;
+                           eases start/stop, turns through three-quarter view, springy lag
+  quadruped(), limb()      jointed legs in diagonal pairs, two-segment limbs
+  stride(), bob(), chain() foot steps, body rise, tapered tails and necks

Applied to farm animals and the farmer, dinosaurs, tundra animals (fox brought down to size), the desert coyote, jungle jaguar and monkey, beach dolphins and crab, the zen heron (at koi scale), city pedestrians and the ocean's reef fish and turtle. Exported from the API and documented.

Evidence

Before (main) on the left, after on the right.

Verification: bun run typecheck passes; CI's check job runs dev/check.ts on this branch.

Merge Danger

Door: two-way

Blast Radius: visuals

Every wallpaper with animals or people.

Merged together with the other visual improvements in #1; this PR's CI screenshot check fails by design because screenshots are regenerated there.