feat(scenes): rich scene descriptions and control viewer window

Add TipTap editing in the editor and an Electron window on the control panel to read the current scene description.

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

app/renderer/editor/sceneDescriptionHtml.test.ts

@@ -0,0 +1,19 @@
+import assert from 'node:assert/strict';
+import test from 'node:test';
+
+import { isSceneDescriptionEmpty, normalizeSceneDescriptionHtml } from './sceneDescriptionHtml';
+
+void test('isSceneDescriptionEmpty treats blank and empty paragraphs as empty', () => {
+  assert.equal(isSceneDescriptionEmpty(''), true);
+  assert.equal(isSceneDescriptionEmpty('   '), true);
+  assert.equal(isSceneDescriptionEmpty('<p></p>'), true);
+  assert.equal(isSceneDescriptionEmpty('<p><br></p>'), true);
+  assert.equal(isSceneDescriptionEmpty('<p>&nbsp;</p>'), true);
+  assert.equal(isSceneDescriptionEmpty('<p>Hi</p>'), false);
+  assert.equal(isSceneDescriptionEmpty('plain'), false);
+});
+
+void test('normalizeSceneDescriptionHtml clears empty markup', () => {
+  assert.equal(normalizeSceneDescriptionHtml('<p></p>'), '');
+  assert.equal(normalizeSceneDescriptionHtml('<p>Ok</p>'), '<p>Ok</p>');
+});