analytical-viz: compound tiebreaker — fewer PEs / lower HBM% when latency ties

Every place that picks a single "best" config from the Pareto set now
uses a compound sort key: (latency_ns ↑, pes_used ↑, hbm_utilization ↑).
Primary = latency; when configs tie on latency (common — cp_ring
variants, some placement variants often produce identical numbers),
prefer smaller-footprint picks.

Places updated:
  - app.py:  sidebar Apply Attn/FFN/Attn+FFN button
  - app.py:  Physical Layout tab Attn/FFN/Attn+FFN button
  - app.py:  Auto Suggest tab "Best latency" metric
  - app.py:  Auto Hardware tab "Best latency" metric (uses parallelism.pes_used
             + parallelism.hbm_utilization since JointScore wraps ConfigScore)
  - auto_hardware.py:  _best_parallelism_for_hw iteration key

No behavior change when there's a strict latency winner. When there are
ties, the picked config uses fewer PEs and lower HBM utilization.

Verified: all 24 pytest tests pass (default include_attention=True and
include_ffn=True paths unchanged).

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

tests/analytical_visualization/auto_hardware.py

@@ -245,14 +245,19 @@ def _best_parallelism_for_hw(
     matches the caller's attention/FFN/full choice.
     """
     best: ConfigScore | None = None
+    best_key: tuple | None = None
     for topo in _iter_reduced_parallelism(model, s_kv, mode):
         cfg = FullConfig(model=model, topo=topo, machine=machine)
         s = score_config(cfg, include_attention=include_attention,
                           include_ffn=include_ffn)
         if not (s.fits_memory and s.placement_valid):
             continue
-        if best is None or s.total_latency_ns < best.total_latency_ns:
+        # Compound tiebreaker: prefer fewer PEs and lower HBM % when latency
+        # ties across variant knobs (cp_ring, placement, kv_shard_mode, etc.).
+        _k = (s.total_latency_ns, s.pes_used, s.hbm_utilization)
+        if best is None or _k < best_key:
             best = s
+            best_key = _k
     return best