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>

tests/ground-inputs.test.ts

@@ -249,3 +249,10 @@ describe('해상 (승인 2026-10-26: MSL 기준, 고조위·저조위 두 개,
     expect(svg).toContain('해저면 EL 28.931');
   });
 });
+
+describe('받침 종류·용량 (글자 입력)', () => {
+  it('is tracked as a change, so it can be reverted to the default', () => {
+    const a = withGround({});
+    expect(changedKeys(a, { ...a, bearingType: '고무받침' })).toEqual(['bearingType']);
+  });
+});