feat(core,view): per-row pile counts 열별 본수 (plan C4)

- A 열 is one row across the footing width; each has its own count along the
  length. Default floor((L − 1400) / 2250) + 1 per 열, as in spec §4.6.
- Counts are validated: one per 열, whole numbers 2–30. Spacing below the
  2250 mm minimum is shown as a warning, not refused (the plan's 6본 → 5@1800
  example).
- PierInput gains an optional pileRows; absent means the defaults, so existing
  files and the P1 results are unchanged.
- Change tracking compares arrays by value; 열별 본수 can be reverted and
  copied (copy item off by default).
- The footing card has −/+ per 열 with spacing, total, and the display string.
- Tests: defaults 4열 × 5본 = 20 and the 1단계 text; 6본 → 5@1800; limits;
  model-level 21 piles.
- Not verified in a browser.

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

src/core/changes.ts

@@ -10,11 +10,21 @@ export const EDITABLE_FIELDS = [
   { key: 'pileLengthMm', label: '말뚝 길이', unit: 'mm' },
 ] as const;
 
-export type EditableKey = (typeof EDITABLE_FIELDS)[number]['key'];
+/** 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'] as const;
 
-/** Keys whose values differ between two inputs. */
+export type EditableKey = (typeof TRACKED_KEYS)[number];
+
+export const FIELD_LABELS: Record<EditableKey, string> = {
+  copingWidthMm: '코핑 폭 B',
+  copingLengthMm: '코핑 길이 L',
+  pileLengthMm: '말뚝 길이',
+  pileRows: '열별 본수',
+};
+
+/** Keys whose values differ between two inputs. Arrays are compared by value. */
 export function changedKeys(a: PierInput, b: PierInput): EditableKey[] {
-  return EDITABLE_FIELDS.map((f) => f.key).filter((key) => a[key] !== b[key]);
+  return TRACKED_KEYS.filter((key) => JSON.stringify(a[key]) !== JSON.stringify(b[key]));
 }
 
 /**