♿️(frontend) improve left panel accessibility (#1262)

Improve overall accessibility of the left panel:
- ⚡️(frontend) make LeftPanelTargetFilter accessible and use Box as nav
- ⚡️(frontend) improve accessibility in left panel components
- ✅(e2e) fix e2e test to expect aria-current instead of aria-selected
- ✨(frontend) add semantic ul/li to LeftPanel
- ✨(frontend) improve favorite item a11y and update e2e test accordingly

src/frontend/apps/e2e/__tests__/app-impress/doc-header.spec.ts

@@ -409,7 +409,7 @@ test.describe('Doc Header', () => {
     const row = await getGridRow(page, docTitle);
 
     // Check is pinned
-    await expect(row.getByLabel('Pin document icon')).toBeVisible();
+    await expect(row.locator('[data-testid^="doc-pinned-"]')).toBeVisible();
     const leftPanelFavorites = page.getByTestId('left-panel-favorites');
     await expect(leftPanelFavorites.getByText(docTitle)).toBeVisible();
 
@@ -424,7 +424,7 @@ test.describe('Doc Header', () => {
     await page.goto('/');
 
     // Check is unpinned
-    await expect(row.getByLabel('Pin document icon')).toBeHidden();
+    await expect(row.locator('[data-testid^="doc-pinned-"]')).toBeHidden();
     await expect(leftPanelFavorites.getByText(docTitle)).toBeHidden();
   });