feat(pipeline): per-instance visibility for batched hatches (Phase 4-B, step 4)

Adds a dedicated `visibility: array<u32>` storage buffer (binding 4)
alongside the existing batched hatch buffers. Vertex shader reads
`visibility[v.instance_index]` — 0 → emit an out-of-NDC clip
position so the GPU rasterizer clips the primitive before the
fragment stage runs.

`compute_hatch_lod` now drives this buffer instead of (or alongside,
for the per-hatch fallback) `hatch_skip_flags`. Walks a per-instance
CPU AABB mirror that the builder fills at upload time (`instance_aabbs`),
applies the same `aabb_below_pixel` (sub-pixel LOD) OR `aabb_offscreen`
(frustum cull) rule the legacy path used, and pushes the resulting
0/1 flags via `queue.write_buffer` on a separate 4 B-per-hatch buffer
— ~40 KB per pan tick for 10 k hatches, far cheaper than re-writing
the 112 B-per-instance data.

Step 5 will remove the legacy `gpu_hatches` Vec, the per-hatch draw
loop, and `hatch_skip_flags` once the batched path has soaked.

Co-Authored-By: Claude Opus 4.7 <[email protected]>

src/scene/render.rs

@@ -147,7 +147,7 @@ impl shader::Primitive for Primitive {
         pipeline.compute_hatch_scissors(self.uniforms.view_proj, clip_size.width, clip_size.height);
         pipeline.compute_wipeout_scissors(self.uniforms.view_proj, clip_size.width, clip_size.height);
         pipeline.compute_image_scissors(self.uniforms.view_proj, clip_size.width, clip_size.height);
-        pipeline.compute_hatch_lod(self.uniforms.view_proj, clip_size.width, clip_size.height);
+        pipeline.compute_hatch_lod(queue, self.uniforms.view_proj, clip_size.width, clip_size.height);
         pipeline.compute_wipeout_lod(self.uniforms.view_proj, clip_size.width, clip_size.height);
         pipeline.compute_mesh_lod(self.uniforms.view_proj, clip_size.width, clip_size.height);
         if self.show_viewcube {