CCL allreduce: rename to lrab_hierarchical_allreduce + descriptive plots

Rename the intercube all-reduce identity to lrab_hierarchical_allreduce
(module, config key, distributed test) so the name reflects both levels
it implements: LRAB intra-SIP (local reduce to center root + broadcast)
and the hierarchical inter-SIP topology exchange (ring/torus/mesh).
ADR-0032 slug kept as the stable decision id; pure rename, no logic change.

Also in this batch:
- ADR-0032 (EN+KO): document the shipped center-root bidirectional reduce
  (doc was stale corner-root); annotate ccl.yaml root_cube as a placeholder.
- Rename allreduce + pe2pe latency plots to descriptive, title-matching
  filenames and retitle the in-plot headings; drop overview/overview_log.
- Point the PPTX image refs at the new plot names.

Doc + derived-artifact + rename only; no simulation behavior changed.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

tests/test_pe_to_pe_diagnostic.py

@@ -472,7 +472,7 @@ def _run_ipcq():
         dst_sip, dst_cube, dst_pe = DST
 
         cfg = load_ccl_config()
-        merged = resolve_algorithm_config(cfg, name="intercube_allreduce")
+        merged = resolve_algorithm_config(cfg, name="lrab_hierarchical_allreduce")
         merged["slot_size"] = max(int(merged.get("slot_size", 4096)), NBYTES)
 
         with RuntimeContext(