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/verify_archives.sh

@@ -0,0 +1,55 @@
+#!/usr/bin/env bash
+# SUM Parts - check the downloaded archives survived
+#
+# The WSL VM has now died twice under load, and the first time it left pip's
+# in-flight files as 0-byte stubs. A download interrupted the same way leaves a
+# truncated zip, so verify before trusting anything that was in flight.
+set -euo pipefail
+
+source "$HOME/miniconda3/etc/profile.d/conda.sh"
+conda activate sumparts
+
+python - <<'PY'
+import zipfile
+from pathlib import Path
+
+d = Path.home() / "sum-parts/data/_archives"
+expected = {"demo.zip": 0.12, "mesh.zip": 0.52, "pcl.zip": 4.66}  # GB, from the HF listing
+
+if not d.exists():
+    print(f"{d} missing")
+    raise SystemExit(1)
+
+bad = []
+for f in sorted(d.glob("*.zip")):
+    gb = f.stat().st_size / 1e9
+    want = expected.get(f.name)
+    line = f"{f.name:<12} {gb:>6.2f} GB"
+    if want:
+        line += f"  (expected ~{want:.2f} GB)"
+        if gb < want * 0.97:
+            line += "  TRUNCATED"
+            bad.append(f.name)
+            print(line)
+            continue
+    try:
+        z = zipfile.ZipFile(f)
+        broken = z.testzip()
+        if broken:
+            line += f"  CORRUPT at {broken}"
+            bad.append(f.name)
+        else:
+            line += f"  OK, {len(z.namelist())} entries"
+    except Exception as e:
+        line += f"  UNREADABLE {type(e).__name__}: {e}"
+        bad.append(f.name)
+    print(line)
+
+for name in expected:
+    if not (d / name).exists():
+        print(f"{name:<12}  MISSING")
+
+print()
+print("all good" if not bad else f"re-download: {', '.join(bad)}")
+raise SystemExit(1 if bad else 0)
+PY