feat(dwg): parse MESH (AcDbSubDMesh) and document the fix

The road-surface drawing (대산당진 2공구_노면) rendered nothing for its
노면/부체도로면 geometry. The cause was not the renderer: the parseResult
contained zero MESH entities.

Two faults, both in the wasm parser, fixed upstream in hmwebviewer 35f5b1c:

1. dwg-wasm never serialized MESH. acadrust reads the entity in full; only the
   JSON arm was missing.

2. acadrust's read_mesh clamped its array counts with the blanket 100_000-item
   corrupt-data guard. This drawing's road mesh has 105_497 vertices, so the
   count was truncated, the remaining vertex bits were never consumed, and the
   face/edge/crease lists after them decoded from the wrong bit offset —
   producing a plausible-looking vertex count next to a nonsense 14-face list.
   Counts are now bounded by the bits actually left in the object stream.

       before  verts=100000 faces=14      face sizes [64, 0, 64, 23, 0, 0, 0, 15]
       after   verts=105497 faces=185444  face sizes [3, 3, 3, ...]

This commit carries the vendored side of that work:

- the rebuilt wasm, which now emits MESH as flat arrays (vertices [x,y,z,...],
  faceList in DXF group-93 layout, deduplicated edges). The sample drawing goes
  from 116 MB to 130 MB of parseResult with parse time unchanged at ~3.2 s.
- a MESH case in the property inspector (vertex/face/edge counts, subdivision
  level, bbox and elevation range)
- docs/subdmesh-rendering.md, plus README pointers
- the acadrust licence notice, which can no longer say "consumed unmodified" —
  read_mesh now carries a local patch. MPL-2.0 is file-level copyleft, so the
  patched file stays under MPL and its source ships in hmwebviewer.

Verified: 9 MESH entities parsed from the drawing; entity histograms over six
other sample drawings are byte-identical to the previous wasm, so nothing else
moved.

Two deliberate omissions, both because a lineweight/fat-line refactor is in
flight in this working tree:

- Viewer2D.js is not included. Its _meshSegs helper and three MESH dispatch
  sites share hunks with that refactor and cannot be separated; the same
  renderer code is committed upstream in hmwebviewer 35f5b1c and will land here
  with the refactor. docs/subdmesh-rendering.md records this.
- dist2/ is not rebuilt here. The current build embeds the half-wired
  lineweight button and progress-bar markup; deploy per
  docs/deploy-dist2-static-build.md once that work lands.

The wasm binary also carries the new lineweight parser fields (lwdisplay,
celweight, layer and entity lineWeight), since it was built from a tree that
already had them. They are additive JSON keys with no consumer in this commit.

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

README.md

@@ -110,6 +110,7 @@ Vite `?url` import 로 로드됩니다.
 | 구형 한글 DWG TEXT 깨짐 (CP949→Latin-1 mojibake) | [`docs/korean-dwg-text-encoding.md`](./docs/korean-dwg-text-encoding.md) |
 | Model + Paper 동시 렌더로 글자 겹침 / Layout 탭 | [`docs/model-paper-space.md`](./docs/model-paper-space.md) |
 | `dist2` 정적 빌드 배포 절차 (공식 배포 스크립트 없음) | [`docs/deploy-dist2-static-build.md`](./docs/deploy-dist2-static-build.md) |
+| SubDMesh(MESH) 미표시 — parseResult 누락 + 큰 메쉬 잘림 | [`docs/subdmesh-rendering.md`](./docs/subdmesh-rendering.md) |
 
 샘플 패치: `fixDwgKoreanText`, `cadSpaces` + Viewer2D 공간 필터, Model/Layout 탭.  
 원본 `hmwebviewer` 반영 절차는 각 문서를 따른다.
@@ -121,6 +122,6 @@ Vite `?url` import 로 로드됩니다.
 | 조각 | 라이선스 |
 |------|----------|
 | Viewer2D 포트 · 샘플 글루 | MIT (hmwebviewer 계열) |
-| acadrust (WASM 내부) | MPL-2.0 |
+| acadrust (WASM 내부, `read_mesh` 로컬 패치 포함) | MPL-2.0 |
 | dxf-parser · three | MIT |
 | NanumGothic | OFL |