analytical-viz: default intra-cube (PE↔PE) BW to 128 GB/s

Was 512 GB/s in the analytical viz MachineParams default. Bringing the
default down to 128 GB/s to match what the modelled physical link now
represents (parity with inter-cube D2D and topology.yaml).

Files touched (all three needed to keep defaults coherent):
  - model_config.py: MachineParams.bw_intra_gbs = 128.0 (was 512.0)
  - app.py: sidebar selectbox default index = 0 (128 GB/s) instead of 2 (512)
  - auto_hardware.py: _HW_KNOB_DEFAULTS + BALANCED + COARSE bw_intra_gbs
    baselines shifted so cost_score at defaults remains 6.0 and the
    sensitivity sweep starts from the new baseline.

Verified: 24 pytest tests pass.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

tests/analytical_visualization/model_config.py

@@ -215,7 +215,7 @@ class MachineParams:
     # HBM per-PE bandwidth (GB/s).
     bw_hbm_gbs: float = 256.0
     # Intra-cube PE↔PE link BW (GB/s).
-    bw_intra_gbs: float = 512.0
+    bw_intra_gbs: float = 128.0
     # Inter-cube (UCIe D2D) BW (GB/s).
     bw_inter_gbs: float = 128.0
     # Inter-SIP (C2C / RDMA) BW (GB/s).