fix(npcs): stop TipTap crash black screen in secondary windows

Guard TipTap getHTML under StrictMode, wrap secondary window roots in WindowErrorBoundary, and add stability regression tests.

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

app/renderer/npcs/tiptapEditorSafe.ts

@@ -0,0 +1,12 @@
+/** Безопасное чтение HTML из TipTap/ProseMirror (StrictMode / destroy mid-flight). */
+export function readTipTapHtmlSafe(editor: {
+  isDestroyed?: boolean;
+  getHTML: () => string;
+} | null | undefined): string | null {
+  if (!editor || editor.isDestroyed) return null;
+  try {
+    return editor.getHTML();
+  } catch {
+    return null;
+  }
+}