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/main.ts

@@ -17,7 +17,7 @@ import { DEFAULT_MATERIAL, FCK_MEMBERS, fyOf, GRADE_CHOICES, isAssumedMaterial,
 import { buildQuantity, quantityRows, type Quantity, type QuantityLine } from './core/rebar/quantity';
 import { parseDrawingRows } from './core/drawing-import';
 import { groundElFor, parseGroundModel, strataRowsFor, type GroundModelFile } from './core/ground-model';
-import { STRATA_NAMES } from './core/ground';
+import { parseNValue, STRATA_NAMES } from './core/ground';
 import { groundSectionSvg } from './view/ground-svg';
 import { parseBearingElevationTable, parseSolplateTable, readDxfTexts } from './core/dxf-table';
 import { columnDiameterIssues } from './core/column-check';
@@ -1582,7 +1582,7 @@ function renderGroundModel(box: HTMLDivElement, pier: Pier): void {
   const table = el('table', undefined, 'grid-table rebar-table');
   const head = el('thead');
   const hr = el('tr');
-  for (const h of ['지층', '하단 EL (m)', '']) hr.appendChild(el('th', h));
+  for (const h of ['지층', '하단 EL (m)', 'N값 (타수 · 타수/관입량 mm)', '']) hr.appendChild(el('th', h));
   head.appendChild(hr);
   table.appendChild(head);
   const body = el('tbody');
@@ -1606,10 +1606,20 @@ function renderGroundModel(box: HTMLDivElement, pier: Pier): void {
     bottomInput.step = '0.001';
     bottomInput.value = String(row.bottomEl);
     bottomInput.addEventListener('change', () => setStrataRows(name, rows.map((r, j) => (j === i ? { ...r, bottomEl: Number(bottomInput.value) } : r))));
+    // N값 as text: a blow count or "타수/관입량 mm" (승인 2026-10-26). Empty means not known yet.
+    const nInput = el('input');
+    nInput.type = 'text';
+    nInput.placeholder = '예: 23 · 50/5';
+    nInput.value = row.nValue ?? '';
+    nInput.addEventListener('change', () => {
+      const v = nInput.value.trim();
+      setStrataRows(name, rows.map((r, j) => (j === i ? { ...r, nValue: v === '' ? undefined : v } : r)));
+    });
+    if (parseNValue(row.nValue).kind === 'invalid') nInput.classList.add('warn-text');
     const del = el('button', '삭제', 'btn small');
     del.type = 'button';
     del.addEventListener('click', () => setStrataRows(name, rows.filter((_, j) => j !== i)));
-    tr.append(...[select, bottomInput, del].map((x) => {
+    tr.append(...[select, bottomInput, nInput, del].map((x) => {
       const td = el('td');
       td.appendChild(x);
       return td;