Record results so far and fix the memory blowup in the palette decode

Adds STATUS.md as the handoff document: benchmark numbers, the bare-earth
metrics that actually matter for this project, the Korean-data domain gap that
retraining will not fix, and what to do on the 24 GB machine.

The memory problem was in how a prediction's colours were turned back into
class indices. Every consumer built an (N, 13, 3) float64 temporary:

    d = ((rgb[:, None, :] - COLOR_MAP[None, :, :]) ** 2).sum(axis=2)

That is ~250 MB of intermediates per 800k-point tile, several live at once, and
a full 4.7M-point block pushes it into gigabytes. main.py writes exact palette
entries, so an exact hash lookup resolves nearly every point with no large
temporary; only leftovers fall back to a chunked distance search. Peak RSS on a
470k-point tile drops to 61 MB. Extracted to sumparts_palette.py and shared by
coarse_eval.py and split_by_class.py.

Also from this round:

- patch_cm_mutation.sh: ConfusionMatrix.update() rewrote the caller's pred
  tensor in place, folding every ignore_index point into class num_classes-1.
  test() saves its visualization from that same tensor afterwards, so an
  unlabelled tile came out 100% wall and the model looked degenerate when it
  was not.
- patch_class_mask.sh: SUMPARTS_MASK_CLASSES drops known-absent classes from
  the argmax. Measured on Seosan and it does not help - the runner-up for
  "water" is "wall", not "terrain" - but the experiment is worth keeping.
- split_by_class.py now writes .ply alongside .obj. A vertex-only OBJ has zero
  faces and most viewers render nothing, which is why the first export looked
  broken.
- verify_outputs.sh reads exported files back with a parser, so "here are your
  files" can be checked rather than asserted.

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

README.md

@@ -1,4 +1,4 @@
-# sum-parts-test
+# sum-parts-test
 
 드론 사진측량 메시를 **건물 / 수목 / 차량 / 지면**으로 분할하기 위한
 [SUM Parts](https://github.com/tudelft3d/SUM-Parts-Benchmarks) (CVPR 2025) 재현 및 적용 작업.
@@ -9,7 +9,8 @@
 
 | 경로 | 내용 |
 |---|---|
-| [SETUP.md](SETUP.md) | **1단계 — 환경 구축 (GPU 불필요). 여기부터** |
+| [STATUS.md](STATUS.md) | **현재 상태·결과·미해결 문제 — 이어받을 때 여기부터** |
+| [SETUP.md](SETUP.md) | 1단계 — 환경 구축 (GPU 불필요) |
 | [TRAIN.md](TRAIN.md) | 2단계 — 학습 (GPU 필요) |
 | [docs/pipeline.html](docs/pipeline.html) | 전체 6단계 공정 정의 (브라우저로 열 것) |
 | [docs/SUM-Parts-검토노트.md](docs/SUM-Parts-검토노트.md) | 트러블슈팅 16건, 데이터 스키마 실측, 라이선스 |