feat(ground): 해상 selectable with MSL levels, 고조위·저조위, and checks

- Rules confirmed (승인 2026-10-26): datum MSL; 고조위 HWL and 저조위 LWL as
  two levels; 세굴 깊이 as for 하상; 파랑과 선박 하중 excluded from this scope.
- Checks: G13 levels missing, G10 해저면 not below 고조위, G11 저조위 not
  below 고조위, G14 pile wall at or below the corrosion allowance reference.
- CORROSION_ALLOWANCE_MM = 1 is a PLACEHOLDER reference (not in the RAG
  documents); the card and G14 mark it as to be confirmed.
- Card: the 해상 inputs; the section draws 고조위 (solid), 저조위 (dashed),
  and labels the ground line 해저면 EL.

Co-Authored-By: Claude Haiku 5.5 <noreply@anthropic.com>

src/core/shape-options.ts

@@ -37,7 +37,7 @@ export const SHAPE_GROUPS: Record<MemberId, ShapeGroup[]> = {
     { title: '말뚝 종류', options: [d('강관'), x('PHC'), x('복합')] },
     { title: '경사말뚝', options: [d('없음'), x('있음')] },
   ],
-  ground: [{ title: '위치', options: [d('육상'), ok('하상'), x('해상')] }],
+  ground: [{ title: '위치', options: [d('육상'), ok('하상'), ok('해상')] }],
 };
 
 export const UNDEFINED_REASON = '규칙 미정 (Q6 확정 전 선택 불가)';