feat(w5): ship v2.0.0 platform sync, undo persistence, and updates

Co-authored-by: Cursor <cursoragent@cursor.com>

src/main/services/undo-stack.service.ts

@@ -0,0 +1,20 @@
+import type { UndoOperation, UndoStackEntry } from '../../shared/undo'
+import { UndoStackRepository } from '../db/repositories/undo.repo'
+import type { SqliteDb } from '../db/types'
+
+export class UndoStackService {
+  constructor(private db: SqliteDb) {}
+
+  push(chapterId: string, operation: UndoOperation): UndoStackEntry {
+    return new UndoStackRepository(this.db).push(chapterId, operation)
+  }
+
+  list(chapterId: string): UndoStackEntry[] {
+    return new UndoStackRepository(this.db).list(chapterId)
+  }
+
+  apply(entryId: number): UndoOperation | null {
+    const entry = new UndoStackRepository(this.db).get(entryId)
+    return entry?.operation ?? null
+  }
+}