chore: phase 2 and 3 refactors

tests/renderer/navigation/sidebarUiPersistence.test.ts

@@ -0,0 +1,14 @@
+import { describe, expect, it } from 'vitest';
+import { getPersistedSidebarSection, setPersistedSidebarSection } from '../../../src/renderer/navigation/sidebarUiPersistence';
+
+describe('sidebarUiPersistence', () => {
+  it('persists and reads section ids by sidebar key', () => {
+    setPersistedSidebarSection('settings', 'project');
+
+    expect(getPersistedSidebarSection('settings')).toBe('project');
+  });
+
+  it('returns null for missing persisted section', () => {
+    expect(getPersistedSidebarSection('tags')).toBeNull();
+  });
+});