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>

ccl.yaml

@@ -6,7 +6,7 @@
 
 defaults:
   # Algorithm to run for this benchmark execution.
-  algorithm: intercube_allreduce
+  algorithm: lrab_hierarchical_allreduce
 
   # IPCQ ring buffer location.
   #   tcm  — PE-local TCM (fast, small, conflicts with compute TCM access)
@@ -37,9 +37,14 @@ algorithms:
   # exchange on root cube, then broadcast back. SIP topology is read
   # from topology.yaml → system.sips.topology. Kernel auto-selects
   # ring / torus / mesh inter-SIP exchange pattern.
-  intercube_allreduce:
-    module: kernbench.ccl.algorithms.intercube_allreduce
+  lrab_hierarchical_allreduce:
+    module: kernbench.ccl.algorithms.lrab_hierarchical_allreduce
     topology: none
     buffer_kind: tcm
     n_elem: 8
+    # root_cube: the kernel currently elects the root dynamically as the
+    # geometric center of the cube mesh (root = (h//2)*w + (w//2)) to
+    # minimize the intra-SIP critical path, so this value is NOT read today.
+    # Kept as a placeholder for a future explicit-root override / runtime
+    # election hook (see ADR-0032 D1 + Non-goals).
     root_cube: 15