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.mjs

@@ -0,0 +1,3 @@
+export default function isPromise(obj) {
+  return !!obj && (typeof obj === 'object' || typeof obj === 'function') && typeof obj.then === 'function';
+}