feat(bearing): 받침 종류·용량 as a text input (default 탄성받침)

- PierInput.bearingType: text, absent = 탄성받침. Tracked for changes, so it
  can be reverted. Saved in the project; no rule yet, so it does not change the model.
- Shown on the ② bearing card above the 공통 규칙.

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', 'highWaterEl', 'lowWaterEl', 'strataRows'] as const;
+export const TRACKED_KEYS = [...EDITABLE_FIELDS.map((f) => f.key), 'pileRows', 'groundPosition', 'groundWaterOn', 'groundWaterEl', 'floodLevelEl', 'scourDepthM', 'highWaterEl', 'lowWaterEl', 'strataRows', 'bearingType'] as const;
 
 export type EditableKey = (typeof TRACKED_KEYS)[number];
 
@@ -51,6 +51,7 @@ export const FIELD_LABELS: Record<EditableKey, string> = {
   scourDepthM: '세굴 깊이',
   highWaterEl: '고조위 HWL',
   lowWaterEl: '저조위 LWL',
+  bearingType: '받침 종류·용량',
   strataRows: '지층 행',
 };