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/project.test.ts

@@ -46,4 +46,21 @@ describe('project file round trip (spec §8, plan B3)', () => {
     expect(() => parseProject(JSON.stringify(broken))).toThrow('교각 2');
     expect(() => parseProject('{ not json')).toThrow('JSON');
   });
+
+  it('keeps defaults and an unregenerated draft through save and open', () => {
+    const original = sampleProject();
+    const p1 = original.piers[0];
+    original.piers[0] = { ...p1, defaults: p1.input, draft: { ...p1.input, copingWidthMm: 3300 } };
+    const reopened = parseProject(serializeProject(original));
+    expect(reopened.piers[0].draft?.copingWidthMm).toBe(3300);
+    expect(reopened.piers[0].input.copingWidthMm).toBe(3100);
+  });
+
+  it('a file saved before change tracking (no defaults or draft) still opens', () => {
+    const legacy = sampleProject();
+    const text = JSON.stringify({ ...legacy, piers: legacy.piers.map((p) => ({ id: p.id, input: p.input })) });
+    const reopened = parseProject(text);
+    expect(reopened.piers[0].defaults).toBeUndefined();
+    expect(reopened.piers[0].draft).toBeUndefined();
+  });
 });