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/changes.ts

@@ -23,7 +23,7 @@ export const EDITABLE_FIELDS = [
 ] as const;
 
 /** Inputs tracked for overrides and pending changes: the numeric cards plus 열별 본수 (an array, compared by value). */
-export const TRACKED_KEYS = [...EDITABLE_FIELDS.map((f) => f.key), 'pileRows', 'groundPosition', 'groundWaterOn', 'groundWaterEl', 'floodLevelEl', 'scourDepthM', 'strataRows'] as const;
+export const TRACKED_KEYS = [...EDITABLE_FIELDS.map((f) => f.key), 'pileRows', 'groundPosition', 'groundWaterOn', 'groundWaterEl', 'floodLevelEl', 'scourDepthM', 'highWaterEl', 'lowWaterEl', 'strataRows'] as const;
 
 export type EditableKey = (typeof TRACKED_KEYS)[number];
 
@@ -49,6 +49,8 @@ export const FIELD_LABELS: Record<EditableKey, string> = {
   groundWaterEl: '지하수위 EL',
   floodLevelEl: '설계홍수위 DHWL',
   scourDepthM: '세굴 깊이',
+  highWaterEl: '고조위 HWL',
+  lowWaterEl: '저조위 LWL',
   strataRows: '지층 행',
 };