feat(assets): apply per-chunk world offset in voxel vertex shader

assets/shaders/cube.vert

@@ -8,10 +8,13 @@ layout(location = 0) out vec3 frag_color;
 
 layout(push_constant) uniform PushConstants {
     mat4 mvp;
+    vec4 chunk_offset;
 } push_constants;
 
 void main() {
-    gl_Position = push_constants.mvp * vec4(in_position, 1.0);
+    // The chunk-local vertex is shifted into world space by the per-chunk offset before projection.
+    vec3 world_position = in_position + push_constants.chunk_offset.xyz;
+    gl_Position = push_constants.mvp * vec4(world_position, 1.0);
 
     frag_color = in_color;
 }