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/edit-mesh-worker.js

@@ -0,0 +1,10 @@
+import {buildEditMesh} from './edit-mesh.js';
+import {loadLightProperties} from './light-properties.js';
+const properties=loadLightProperties();
+self.onmessage=({data})=>properties.then(table=>{
+  const start=performance.now(),result={id:data.id,epoch:data.epoch,editJob:data.editJob,preview:true};
+  try {
+    const mesh=buildEditMesh(data,table);
+    self.postMessage({...result,...mesh,milliseconds:performance.now()-start},[mesh.vertices.buffer,mesh.transparent.buffer]);
+  } catch(error) {self.postMessage({...result,error:error.message});}
+}).catch(error=>self.postMessage({id:data.id,epoch:data.epoch,editJob:data.editJob,error:error.message}));