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/app.py

@@ -374,7 +374,7 @@ with st.sidebar.expander("Hardware", expanded=False):
             bw_intra = st.selectbox(
                 "intra-cube GB/s",
                 [128.0, 256.0, 512.0, 1024.0, 2048.0, 4096.0],
-                index=2, key="bw_intra",
+                index=0, key="bw_intra",
             )
             bw_inter = st.selectbox(
                 "inter-cube GB/s",