feat(core,view): input cards with change tracking (plan B1 · C2)

- Three values per pier: defaults (as imported), input (generated), draft
  (current cards). Overrides = draft vs defaults; pending = draft vs input.
- Editable now: 코핑 폭, 코핑 길이, 말뚝 길이. Changing a card does not touch the
  3D view until 다시 생성; the header and the card show 변경 n.
- Revert puts a field back to its imported default.
- Project files store defaults and draft (optional; v1 files still open).
- Tests: 코핑 폭 3100 → 3300 gives one override and one pending change;
  regenerating clears pending but keeps the override; revert; file round trip.
- Not verified in a browser (no debuggable Chrome in this session).

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

tests/changes.test.ts

@@ -0,0 +1,42 @@
+import { describe, expect, it } from 'vitest';
+import { buildPier } from '../src/core/geometry';
+import { overrideKeys, pendingKeys, revertDraft, type PierValues } from '../src/core/changes';
+import { loadP1 } from './helpers';
+
+function fresh(): PierValues {
+  const input = loadP1();
+  return { defaults: input, input, draft: input };
+}
+
+describe('input change tracking (plan B1 · C2)', () => {
+  it('a new pier has no overrides and nothing pending', () => {
+    const p = fresh();
+    expect(overrideKeys(p)).toEqual([]);
+    expect(pendingKeys(p)).toEqual([]);
+  });
+
+  it('coping width 3100 → 3300: one override and one pending change', () => {
+    const p = fresh();
+    const next = { ...p, draft: { ...p.draft, copingWidthMm: 3300 } };
+    expect(overrideKeys(next)).toEqual(['copingWidthMm']);
+    expect(pendingKeys(next)).toEqual(['copingWidthMm']);
+  });
+
+  it('regenerating clears the pending change but keeps the override', () => {
+    const p = fresh();
+    const edited = { ...p, draft: { ...p.draft, copingWidthMm: 3300 } };
+    const regenerated: PierValues = { ...edited, input: edited.draft };
+    expect(pendingKeys(regenerated)).toEqual([]);
+    expect(overrideKeys(regenerated)).toEqual(['copingWidthMm']);
+    expect(buildPier(regenerated.input).copingB).toBeCloseTo(3.3, 9);
+  });
+
+  it('reverting to the default removes the override', () => {
+    const p = fresh();
+    const edited = { ...p, draft: { ...p.draft, copingWidthMm: 3300 } };
+    const reverted = { ...edited, draft: revertDraft(edited, 'copingWidthMm') };
+    expect(overrideKeys(reverted)).toEqual([]);
+    // The draft is back to the generated value, so nothing is pending either.
+    expect(pendingKeys(reverted)).toEqual([]);
+  });
+});