feat(notebook): m009 sort_order 컬럼 + reorder 메서드 + IPC notebook:reorder

- m009 마이그레이션: notebooks.sort_order INTEGER 컬럼 추가, 기존 rows created_at 순으로 backfill
- NotebookRepository.list ORDER BY sort_order ASC, name ASC 로 변경
- NotebookRepository.create 신규 노트북 sort_order = max+1 자동 할당
- NotebookRepository.reorder(id, direction) — swap transaction 으로 atomic 순서 변경
- IPC notebook:reorder 핸들러 등록, preload/shared types pass-through
- 테스트 45개 추가 (m009, reorder 케이스 4, list ORDER BY, IPC 핸들러 2)

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

tests/unit/notebookApi.test.ts

@@ -22,7 +22,8 @@ function makeRepo() {
     setColor: vi.fn(),
     delete: vi.fn(() => ({ ok: true })),
     moveNote: vi.fn(),
-    findById: vi.fn(() => null)
+    findById: vi.fn(() => null),
+    reorder: vi.fn(() => ({ ok: true }))
   };
 }
 
@@ -96,4 +97,23 @@ describe('notebookApi IPC', () => {
     expect(repo.setColor).toHaveBeenCalledWith('id1', '#fff');
     expect(r).toEqual({ ok: true });
   });
+
+  it('notebook:reorder — repo.reorder 호출 + ok:true 전달', async () => {
+    const repo = makeRepo();
+    repo.reorder.mockReturnValue({ ok: true } as never);
+    registerNotebookApi({ repo: repo as never });
+    const h = getHandler('notebook:reorder');
+    const r = await h({}, 'nb-1', 'up');
+    expect(repo.reorder).toHaveBeenCalledWith('nb-1', 'up');
+    expect(r).toEqual({ ok: true });
+  });
+
+  it('notebook:reorder — 첫 번째 항목 up 시 ok:false 전달', async () => {
+    const repo = makeRepo();
+    repo.reorder.mockReturnValue({ ok: false } as never);
+    registerNotebookApi({ repo: repo as never });
+    const h = getHandler('notebook:reorder');
+    const r = await h({}, 'nb-first', 'up');
+    expect(r).toEqual({ ok: false });
+  });
 });