feat(editor): add About menu with app info and user guide

Add header menu with About and Instructions modals so GMs can read product details and step-by-step help for all app features.

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

app/renderer/editor/help/helpSections.ts

@@ -0,0 +1,28 @@
+/** Порядок разделов в окне «Инструкция». */
+export const HELP_SECTION_IDS = [
+  'overview',
+  'license',
+  'projects',
+  'scenes',
+  'graph',
+  'sceneProps',
+  'campaignAudio',
+  'session',
+  'controlPanel',
+  'transitions',
+  'music',
+  'effects',
+  'presentation',
+  'importExport',
+  'settings',
+] as const;
+
+export type HelpSectionId = (typeof HELP_SECTION_IDS)[number];
+
+export function helpSectionTitleKey(id: HelpSectionId): string {
+  return `help.section.${id}.title`;
+}
+
+export function helpSectionBodyKey(id: HelpSectionId): string {
+  return `help.section.${id}.body`;
+}