refactor(ground): remove the unversioned-file fallback

- A file without a schema number is refused again; the example output in
  RAG/pierzainer_ground now has schema 2, so the temporary path is not needed.
- The legacy fixture is removed; tests cover the missing and null schema
  numbers and a pier without a ground object.

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

tests/ground-model.test.ts

@@ -1,4 +1,3 @@
-import { readFileSync } from 'node:fs';
 import { describe, expect, it } from 'vitest';
 import { groundElFor, parseGroundModel } from '../src/core/ground-model';
 import { changedKeys, overrideKeys, revertDraft, type PierValues } from '../src/core/changes';
@@ -89,26 +88,17 @@ describe('지형 격자 (schema 2)', () => {
   });
 });
 
-describe('번호 없는 옛 지반 모델 (B′: 임시 경로)', () => {
-  // examples/out/ground_model.json as written before the schema number existed (P1–P6, same values as the report).
-  const LEGACY = readFileSync(new URL('./fixtures/ground-model-legacy.json', import.meta.url), 'utf-8');
-
-  it('reads the unversioned file and reports it as schema 1', () => {
-    const m = parseGroundModel(LEGACY);
-    expect(m.schema).toBe(2);                                // normalised to the current schema
-    expect(m.piers.map((p) => p.id)).toEqual(['P1', 'P2', 'P3', 'P4', 'P5', 'P6']);
-    expect(groundElFor(m, 'P1')).toBe(29.355);
-    expect(m.piers[0].excelEl).toBe(28.931);
+describe('형식 번호 검사', () => {
+  it('refuses a file with no schema number (the B′ fallback is removed)', () => {
+    expect(() => parseGroundModel(JSON.stringify({ piers: [{ id: 'P1', ground: { center: 29.355, excel: 28.931 } }] }))).toThrow('형식 번호 undefined');
   });
 
-  it('refuses a pier that has no ground object (a renamed field must not load as empty values)', () => {
-    const data = JSON.parse(LEGACY);
-    delete data.piers[1].ground;
-    expect(() => parseGroundModel(JSON.stringify(data))).toThrow('P2: 지반 값(ground)이 없습니다');
+  it('refuses a null schema number', () => {
+    expect(() => parseGroundModel('{"schema": null, "piers": []}')).toThrow('형식 번호 null');
   });
 
-  it('refuses a null schema number instead of treating it as missing', () => {
-    expect(() => parseGroundModel(LEGACY.replace('{', '{"schema": null,'))).toThrow('형식 번호 null');
+  it('refuses a pier that has no ground object', () => {
+    expect(() => parseGroundModel(JSON.stringify({ schema: 1, piers: [{ id: 'P2' }] }))).toThrow('P2: 지반 값(ground)이 없습니다');
   });
 });