docs(bench_latency): correct max-vs-heap-head comment

The previous wording called `percentile(1.0)` "the top-K head", which
is misleading for a min-heap implementation: `topKHeap[0]` is the
SMALLEST element in the top-K (the admission threshold for new
outliers), not the largest. The implementation snapshots the heap
into a sequence, sorts it, and returns `topk[^1]` — the maximum.

Comment-only change; behaviour unchanged.

Author: elijahr

benchmarks/nim/bench_latency.nim

@@ -154,7 +154,10 @@ proc runVariant(
   # (Task 6.2) sits well above the 100-sample p999 tail at the default
   # MessageCount and reserves headroom for larger MessageCount overrides
   # before p999 spills into the rescaled-reservoir stratum. max is
-  # `percentile(1.0)`, always the top-K head.
+  # `percentile(1.0)`, which after sorting the snapshotted top-K returns
+  # `topk[^1]` (the largest element). This is NOT the heap head: the
+  # min-heap's root (`topKHeap[0]`) is the SMALLEST of the top-K, the
+  # admission threshold for new outliers, not the maximum sample seen.
   em.addMeasure(slug, "latency_p999_ns", metrics.p999_ns)
   em.addMeasure(slug, "latency_max_ns", metrics.max_ns)