ui: tweak ModelCard buttons + topology summary + dummy-run fixture

ModelCard:
- Move Metrics out of the always-visible header pill row and into the
  click-expand action area as a "Metrics Dashboard" button next to
  OpenWebUI. Same shape, same affordance — both are model actions.
- Open-in-OpenWebUI button restyled to bg-black for a quieter primary.
- Header device line replaces a flat distinct-device list with a
  topologySummary() across replicas: if every replica has the same
  shape (almost always), show it once ("2 nodes × 4x NVIDIA GH200");
  if they differ, show "Various" rather than picking one to display.

Dummy-run fixture:
- Replace the synthesised dnt_table_upgraded.json (which generated
  artefacts like x10 replica counts and a 43-replica total) with a
  live dev-mesh snapshot dnt_table_dev_live.json. 11 real peers
  including multi-node replicas — exercises the topology summary,
  shared-worker_group_id grouping, and the new framework_args /
  expires_at labels. The synthesised fixture stays on disk for the
  build_upgraded.py generator + unit tests that depend on it.

Author: robmsmt

Makefile

@@ -78,7 +78,7 @@ run: _ensure-env _ensure-frontend-env db-up migrate
 # upgraded fixture instead of the live OpenTela endpoint. Useful for
 # iterating on the model-card UI without depending on prod state.
 dummy-run: _ensure-env _ensure-frontend-env db-up migrate
-	OTELA_FIXTURE_PATH=$(PWD)/backend/tests/fixtures/dnt_table_upgraded.json \
+	OTELA_FIXTURE_PATH=$(PWD)/backend/tests/fixtures/dnt_table_dev_live.json \
 	uvicorn backend.main:app --reload --host 0.0.0.0 --port 8080 & \
 	cd frontend && npm run dev & \
 	wait