Show individual routers in cube_view SVG, fix row Y overlap

- cube_view now renders all 32 router nodes from cube_mesh.yaml
  instead of collapsed "router_mesh" placeholder
- Fix mesh_gen row Y position overlap (r1/r2 and r3/r4 had same Y)
  by adding hbm_gap spacing between PE rows and HBM zone
- Add noc_router to visualizer KIND_SIZE for proper sizing
- Update cube view tests for individual router nodes

339 passed

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/kernbench/topology/visualizer.py

@@ -62,6 +62,7 @@ _KIND_SIZE: dict[str, tuple[float, float]] = {
     "cube": (6.0, 4.0),
     "iochiplet": (4.0, 1.5),
     "switch": (5.0, 1.5),
+    "noc_router": (1.2, 0.8),
 }