Revert "ifcviewer: GPU LOD0/LOD1 selection in compute cull (step 3c)"

This reverts commit 77cac3ec170b622db6977829f66b62603266a047.

src/ifcviewer/README.md

@@ -795,18 +795,14 @@ single giant model / <18 cores  CPU BVH trv             Phase 3E GPU cull (plann
 - [x] Event-driven rendering (zero idle CPU/GPU, cull skipped on still frames)
 - [~] **Phase 3E — GPU-side compute-shader culling** (in progress)
       - [x] 3a: `IFC_GPU_CULL=1` drives rendering via compute cull (frustum +
-            contribution).  Perf regressed — submits one sub-draw per mesh
-            even when `instanceCount=0` (CP overhead from empty commands).
-      - [x] 3b: fwd/rev reflection bucketing — compact shader routes by
-            reflected flag into CCW and CW MDI buckets.
-      - [x] 3c: LOD0/LOD1 selection — compact shader computes per-instance
-            pixel radius and routes to LOD1 bucket when below threshold.
-            Per-mesh `has_lod1` flags SSBO.  4 buckets per mesh (fwd/rev ×
-            LOD0/LOD1), 4M commands total, 2 MDIs per model.
+            contribution, single bucket per mesh).  Correctness matches CPU
+            path; perf regressed — we submit one sub-draw per mesh even
+            when `instanceCount=0`.  Fix is MDI compaction via
+            `glMultiDrawElementsIndirectCount`, deferred to 3a-followup so
+            we don't pull a GL 4.6 entrypoint loader into this commit.
+      - [ ] 3a-followup: compact non-empty commands, use count-buffer MDI
+      - [ ] 3b: fwd/rev reflection bucketing on GPU
+      - [ ] 3c: LOD0/LOD1 selection on GPU
       - [ ] 3d: HiZ with same-frame depth pre-pass
-      - [ ] MDI compaction — compact non-empty commands into contiguous
-            buffer, use `glMultiDrawElementsIndirectCount` (GL 4.6 /
-            `ARB_indirect_parameters`).  Deferred until all feature buckets
-            land so we can introduce GL 4.6 loading once, cleanly.
 - [ ] Vulkan/MoltenVK backend for macOS
 - [ ] Embedded Python scripting console