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/migrations.test.ts

@@ -51,11 +51,11 @@ describe('migration v3 — soft delete columns', () => {
     db.close();
   });
 
-  it('user_version reaches latest (8)', () => {
+  it('user_version reaches latest (9)', () => {
     const db = new Database(':memory:');
     runMigrations(db);
     const row = db.prepare('PRAGMA user_version').get() as { user_version: number };
-    expect(row.user_version).toBe(8);
+    expect(row.user_version).toBe(9);
     db.close();
   });