fix: Add debounced Undo/Redo system to avoid character-by-character history

- Add debounced state updates for title and content (500ms delay)
- Immediate UI updates with delayed history saving
- Prevent one-letter-per-undo issue
- Add cleanup for debounce timers on unmount

mcp-server/node_modules/is-promise/index.d.ts

@@ -0,0 +1,2 @@
+declare function isPromise<T, S>(obj: PromiseLike<T> | S): obj is PromiseLike<T>;
+export default isPromise;