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/diag_run.sh

@@ -0,0 +1,28 @@
+#!/usr/bin/env bash
+# SUM Parts - dump everything about the most recent run attempt
+set -uo pipefail
+
+RUNROOT="$HOME/sum-parts/runs"
+D="${1:-$(cat "$RUNROOT/.latest" 2>/dev/null)}"
+
+echo "run dir: $D"
+[ -d "$D" ] || { echo "  (missing)"; exit 1; }
+ls -la "$D"
+
+for f in watchdog.log nohup.out status.txt train.log; do
+    echo
+    echo "=== $f ==="
+    if [ -f "$D/$f" ]; then
+        tail -30 "$D/$f"
+    else
+        echo "  (absent)"
+    fi
+done
+
+echo
+echo "=== processes ==="
+pgrep -af 'train_watchdog|main.py' || echo "  none running"
+
+echo
+echo "=== syntax check of watchdog ==="
+bash -n /mnt/d/MYCLAUDE_PROJECT/sum-parts-test/scripts/train_watchdog.sh && echo "  OK"