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>

src/main/repository/NotebookRepository.ts

@@ -11,7 +11,7 @@ export class NotebookRepository {
               (SELECT COUNT(*) FROM notes n
                 WHERE n.notebook_id = nb.id AND n.status = 'active') AS note_count
          FROM notebooks nb
-        ORDER BY nb.name ASC`
+        ORDER BY nb.sort_order ASC, nb.name ASC`
     ).all() as Array<Record<string, unknown>>;
     return rows.map((r) => this.hydrate(r));
   }
@@ -30,12 +30,31 @@ export class NotebookRepository {
   create(input: { name: string; color?: string | null }): Notebook {
     const id = uuidv7();
     const now = new Date().toISOString();
+    const maxRow = this.db.prepare(`SELECT COALESCE(MAX(sort_order), -1) AS m FROM notebooks`).get() as { m: number };
+    const sortOrder = maxRow.m + 1;
     this.db.prepare(
-      `INSERT INTO notebooks(id, name, color, created_at, updated_at) VALUES(?,?,?,?,?)`
-    ).run(id, input.name, input.color ?? null, now, now);
+      `INSERT INTO notebooks(id, name, color, created_at, updated_at, sort_order) VALUES(?,?,?,?,?,?)`
+    ).run(id, input.name, input.color ?? null, now, now, sortOrder);
     return { id, name: input.name, color: input.color ?? null, createdAt: now, updatedAt: now, noteCount: 0 };
   }
 
+  reorder(id: string, direction: 'up' | 'down'): { ok: boolean } {
+    const cur = this.db.prepare(`SELECT sort_order FROM notebooks WHERE id = ?`).get(id) as { sort_order: number } | undefined;
+    if (!cur) return { ok: false };
+    const neighbor = direction === 'up'
+      ? this.db.prepare(`SELECT id, sort_order FROM notebooks WHERE sort_order < ? ORDER BY sort_order DESC LIMIT 1`).get(cur.sort_order)
+      : this.db.prepare(`SELECT id, sort_order FROM notebooks WHERE sort_order > ? ORDER BY sort_order ASC LIMIT 1`).get(cur.sort_order);
+    if (!neighbor) return { ok: false };  // 이미 끝
+    const n = neighbor as { id: string; sort_order: number };
+    const now = new Date().toISOString();
+    const tx = this.db.transaction(() => {
+      this.db.prepare(`UPDATE notebooks SET sort_order = ?, updated_at = ? WHERE id = ?`).run(n.sort_order, now, id);
+      this.db.prepare(`UPDATE notebooks SET sort_order = ?, updated_at = ? WHERE id = ?`).run(cur.sort_order, now, n.id);
+    });
+    tx();
+    return { ok: true };
+  }
+
   rename(id: string, name: string): void {
     const now = new Date().toISOString();
     this.db.prepare(`UPDATE notebooks SET name=?, updated_at=? WHERE id=?`).run(name, now, id);