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/epoch_timing.sh

@@ -0,0 +1,35 @@
+#!/usr/bin/env bash
+# SUM Parts - per-epoch wall time, to locate where a run slowed down
+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 $WORKDIR"; exit 1; }
+
+grep -E 'Epoch [0-9]+ LR' "$LOG" | awk '
+{
+    # [08/20 20:28:44 SUMV2_Triangle]: Epoch 10 LR ...
+    #  $1      $2         $3           $4    $5
+    split($2, t, ":")
+    sec = t[1]*3600 + t[2]*60 + t[3]
+    for (i = 1; i <= NF; i++) if ($i == "Epoch") { ep = $(i+1); break }
+    if (prev_sec != "") {
+        d = sec - prev_sec
+        if (d < 0) d += 86400          # crossed midnight
+        printf "epoch %3d  %s  +%6.1f s", ep, t[1]":"t[2]":"t[3], d
+        if (d > slow_thresh) printf "   <-- SLOW"
+        printf "\n"
+    } else {
+        printf "epoch %3d  %s\n", ep, t[1]":"t[2]":"t[3]
+    }
+    prev_sec = sec
+}
+BEGIN { slow_thresh = 300 }
+'
+
+echo
+echo "--- summary ---"
+grep -E 'Epoch [0-9]+ LR' "$LOG" | tail -1
+echo "epochs done: $(grep -cE 'Epoch [0-9]+ LR' "$LOG")"