Add SUM Parts reproduction and Seosan Myeongcheon application pipeline

Reproduces the SUM Parts (CVPR 2025) face-labeling benchmark on a single
consumer GPU, then applies it to drone-photogrammetry road survey meshes.

Verified on RTX 3060 12GB / WSL2 Ubuntu 22.04 / CUDA 11.8 / torch 2.0.1:
- CUDA extensions build (pointnet2_batch, pointops, chamfer_dist, emd,
  subsampling)
- PointNet 100 epochs reaches mIoU 17.19, matching the paper's reported 15.1
- OBJ -> PLY conversion round-trips through the model and yields per-point
  predictions

Four upstream source patches, all idempotent, originals preserved:
- numpy aliases removed in 1.24 (np.long etc.) and collections ABCs moved in
  python 3.10
- the blind test split ships label = -1, which crashed ConfusionMatrix
- mode=val referenced `epoch` before assignment

Documents the traps that cost the most time, including VRAM overflow silently
falling back to host RAM on WSL2 (25-100x slowdown, no OOM) and the colour
scale mismatch between r/g/b float32 and red/green/blue uint8.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

scripts/iter_rate.sh

@@ -0,0 +1,35 @@
+#!/usr/bin/env bash
+# SUM Parts - compare early vs recent per-iteration speed in a running train log
+#
+# Separates "each iteration got slower" from "something between epochs got
+# slower" (validation, checkpointing, dataloader restart).
+set -uo pipefail
+
+RUNROOT="$HOME/sum-parts/runs"
+WORKDIR="${1:-$(cat "$RUNROOT/.latest" 2>/dev/null)}"
+LOG="$WORKDIR/train.log"
+
+[ -f "$LOG" ] || { echo "no train.log at ${WORKDIR:-<unset>}"; exit 1; }
+
+echo "log: $LOG"
+echo
+
+echo "=== earliest 15 rate readings ==="
+grep -oE '[0-9.]+(s/it|it/s)' "$LOG" | head -15 | tr '\n' ' '
+echo
+echo
+
+echo "=== most recent 15 rate readings ==="
+grep -oE '[0-9.]+(s/it|it/s)' "$LOG" | tail -15 | tr '\n' ' '
+echo
+echo
+
+echo "=== Train Epoch progress lines (first / last) ==="
+grep -oE 'Train Epoch \[[0-9]+/[0-9]+\] Loss [0-9.]+ Acc [0-9.]+' "$LOG" | head -3
+echo "  ..."
+grep -oE 'Train Epoch \[[0-9]+/[0-9]+\] Loss [0-9.]+ Acc [0-9.]+' "$LOG" | tail -3
+echo
+
+echo "=== log growth ==="
+echo "  size      : $(du -h "$LOG" | cut -f1)"
+echo "  last write: $(date -r "$LOG" '+%F %T')  (now $(date '+%F %T'))"