fix(e2e): update tests to match current UI and fix panel persistence

Code:
- Persist panelOpen to localStorage so panel stays open after reload
- Auto-open panel to Metadaten when document has no file (no prior state)

Tests:
- Nav active state: check bg-nav-active instead of text-brand-navy
  (nav uses semantic tokens since dark mode refactor)
- Save button: use exact:true to avoid matching "Speichern & abschließen"
  (new button was added alongside the plain "Speichern" button)

Note: annotation tests (documents.spec.ts:324, 356) are pre-existing
flaky failures due to test data contamination, not caused by this PR.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/e2e/history.spec.ts

@@ -25,7 +25,7 @@ test.describe('Document history panel', () => {
 		await page.goto('/documents/new');
 		await page.waitForSelector('[data-hydrated]');
 		await page.getByLabel('Titel').fill('E2E History Test Dokument');
-		await page.getByRole('button', { name: /Speichern/i }).click();
+		await page.getByRole('button', { name: 'Speichern', exact: true }).click();
 		// Wait for redirect to the new document's UUID-based URL (not /documents/new)
 		await page.waitForURL(/\/documents\/[0-9a-f-]{36}$/);
 		docPath = new URL(page.url()).pathname;
@@ -34,7 +34,7 @@ test.describe('Document history panel', () => {
 		await page.goto(`${docPath}/edit`);
 		await page.waitForSelector('[data-hydrated]');
 		await page.getByLabel('Titel').fill('E2E History Test Dokument (bearbeitet)');
-		await page.getByRole('button', { name: /Speichern/i }).click();
+		await page.getByRole('button', { name: 'Speichern', exact: true }).click();
 		await page.waitForURL(/\/documents\/[0-9a-f-]{36}$/);
 
 		await context.close();