Expand voxel gameplay, lighting, full-height streaming and world imports

Add shared Rust/WASM physics, worker meshing and diagnostics, 64-chunk full-height streaming, atlas texture support, and baseline world import. Document the current implementation and include the supplied in-game lobby screenshot.

client/tests/player-avatar.test.js

@@ -0,0 +1,39 @@
+import test from "node:test";
+import assert from "node:assert/strict";
+import { playerAvatarParts } from "../renderer.js";
+
+test("remote avatar stance and eye placement follow server physics dimensions", () => {
+  for (const [pose, height, eye_height] of [
+    ["standing", 1.8, 1.62],
+    ["crouching", 1.5, 1.27],
+    ["swimming", 0.6, 0.4],
+  ]) {
+    const parts = playerAvatarParts({ pose, height, eye_height });
+    assert.equal(Math.max(...parts.map(({ box }) => box.max[1])), height);
+    const head = parts.find(({ part }) => part === "head").box;
+    const eyes = parts.find(({ part }) => part === "eyes").box;
+    assert.ok(Math.abs((eyes.min[1] + eyes.max[1]) / 2 - eye_height) < 1e-12);
+    assert.ok(eyes.min[1] >= head.min[1] && eyes.max[1] <= head.max[1]);
+    for (const { box } of parts)
+      for (let axis = 0; axis < 3; axis++) {
+        assert.ok(
+          Number.isFinite(box.min[axis]) && box.max[axis] > box.min[axis],
+        );
+      }
+  }
+});
+
+test("swimming and crawling use a horizontal silhouette while crouching leans forward", () => {
+  const standing = playerAvatarParts({});
+  const crouching = playerAvatarParts({ pose: "crouching" });
+  const swimming = playerAvatarParts({ pose: "swimming" });
+  const head = (parts) => parts.find(({ part }) => part === "head").box;
+  assert.ok(head(crouching).min[2] < head(standing).min[2]);
+  const length =
+    Math.max(...swimming.map(({ box }) => box.max[2])) -
+    Math.min(...swimming.map(({ box }) => box.min[2]));
+  assert.ok(length > 1.6);
+  assert.ok(Math.max(...swimming.map(({ box }) => box.max[1])) <= 0.6);
+  assert.equal(swimming.filter(({ part }) => part === "leg").length, 2);
+  assert.equal(swimming.filter(({ part }) => part === "arm").length, 2);
+});