perf(mdviewer): reduce content sync debounce for snappier typing

- viewer → CM: 300ms → 50ms (CONTENT_CHANGE_DEBOUNCE)
- CM → viewer: 150ms → 50ms (DEBOUNCE_TO_IFRAME_MS)

Author: abose

src-mdviewer/src/components/editor.js

@@ -1566,7 +1566,7 @@ export function convertToMarkdown(contentEl) {
 
 // Debounced content change emitter for bridge
 let contentChangeTimer = null;
-const CONTENT_CHANGE_DEBOUNCE = 300;
+const CONTENT_CHANGE_DEBOUNCE = 50;
 
 /**
  * Re-compute data-source-line attributes on top-level block elements

src/extensionsIntegrated/Phoenix-live-preview/MarkdownSync.js

@@ -55,7 +55,7 @@ define(function (require, exports, module) {
     let _cursorUndoStack = [];
     let _cursorRedoStack = [];
 
-    const DEBOUNCE_TO_IFRAME_MS = 150;
+    const DEBOUNCE_TO_IFRAME_MS = 50;
     const SCROLL_SYNC_DEBOUNCE_MS = 16;
     const SELECTION_SYNC_DEBOUNCE_MS = 200;