feat(ground): 하상 selectable; 설계홍수위 and 세굴 깊이 for 하상

- shape-options: a per-option "confirmed" flag; 하상 is confirmed, 해상 is not.
- The 위치 chips store the choice in the pier's draft; 선택 shows it.
- 하상: the groundwater inputs give way to 설계홍수위 DHWL (floodLevelEl) and
  세굴 깊이 (scourDepthM). The groundwater value is kept (남겨두기).
- Checks: G07 DHWL missing, G08 DHWL below the 지반고, G09 scour negative or
  the scour line below the footing bottom. The groundwater check is skipped for 하상.
- Section: the DHWL as a solid line and the 세굴선 dashed.

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', 'strataRows'] as const;
+export const TRACKED_KEYS = [...EDITABLE_FIELDS.map((f) => f.key), 'pileRows', 'groundPosition', 'groundWaterOn', 'groundWaterEl', 'floodLevelEl', 'scourDepthM', 'strataRows'] as const;
 
 export type EditableKey = (typeof TRACKED_KEYS)[number];
 
@@ -47,6 +47,8 @@ export const FIELD_LABELS: Record<EditableKey, string> = {
   groundPosition: '지반 위치',
   groundWaterOn: '지하수위 고려',
   groundWaterEl: '지하수위 EL',
+  floodLevelEl: '설계홍수위 DHWL',
+  scourDepthM: '세굴 깊이',
   strataRows: '지층 행',
 };