feat(chat): add local-first conversation workspace

chat/lib/fullscreen-editor.ts

@@ -0,0 +1,8 @@
+export const fullscreenEditorCharacterThreshold = 600;
+export const fullscreenEditorLineThreshold = 8;
+
+export function shouldOpenFullscreenEditor(value: unknown) {
+  const text = String(value ?? "");
+  const lineCount = text ? text.split(/\r?\n/).length : 0;
+  return text.length >= fullscreenEditorCharacterThreshold || lineCount >= fullscreenEditorLineThreshold;
+}