feat(ground): N value per layer row (text, blow count or 타수/관입량 mm)

- StrataRow.nValue: text. "23" is a blow count (0–100), "50/5" a refusal
  (50 blows for 5 mm, 1–300 mm). Empty means not known yet.
- G06 (warning): a malformed N value. Strict, because the values will feed the
  bearing-capacity and liquefaction checks.
- The layer table has an N값 column; the project file checks that the rows
  are well formed.

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

src/core/project.ts

@@ -75,6 +75,11 @@ export function parseProject(text: string): ProjectFile {
   obj.piers.forEach((p, i) => {
     if (!p || typeof p.id !== 'string' || !p.input) throw new Error(`교각 ${i + 1}: id 또는 input이 없습니다.`);
     const input = p.input;
+    const rows = input.strataRows;
+    if (rows !== undefined) {
+      const ok = Array.isArray(rows) && rows.every((r) => typeof r?.name === 'string' && typeof r?.bottomEl === 'number' && Number.isFinite(r.bottomEl) && (r.nValue === undefined || typeof r.nValue === 'string'));
+      if (!ok) throw new Error(`교각 ${input.name}: 지층 행 형식이 맞지 않습니다.`);
+    }
     if (typeof input.name !== 'string' || !Array.isArray(input.ips) || !Array.isArray(input.bearings)) {
       throw new Error(`교각 ${i + 1}(${String(input.name)}): 입력 형식이 맞지 않습니다.`);
     }