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/src/routes/documents/[id]/+page.svelte

@@ -67,6 +67,7 @@ $effect(() => {
 
 const LS_KEY_HEIGHT = 'doc-panel-height';
 const LS_KEY_TAB = 'doc-panel-tab';
+const LS_KEY_OPEN = 'doc-panel-open';
 
 let panelOpen = $state(false);
 let panelHeight = $state(0); // set to full height on mount
@@ -79,6 +80,7 @@ onMount(() => {
 
 	const savedHeight = localStorage.getItem(LS_KEY_HEIGHT);
 	const savedTab = localStorage.getItem(LS_KEY_TAB);
+	const savedOpen = localStorage.getItem(LS_KEY_OPEN);
 
 	if (savedTab && ['metadata', 'transcription', 'discussion', 'history'].includes(savedTab)) {
 		activeTab = savedTab as DocumentPanelTab;
@@ -90,6 +92,14 @@ onMount(() => {
 		if (!isNaN(h) && h >= 80) panelHeight = h;
 	}
 
+	if (savedOpen === 'true') {
+		panelOpen = true;
+	} else if (savedOpen === null && !doc?.filePath) {
+		// No prior state and no file — open to metadata so the panel is immediately useful.
+		panelOpen = true;
+		activeTab = 'metadata';
+	}
+
 	localStorageRestored = true;
 
 	function onKeyDown(e: KeyboardEvent) {
@@ -111,6 +121,7 @@ $effect(() => {
 	if (!localStorageRestored) return;
 	localStorage.setItem(LS_KEY_HEIGHT, String(panelHeight));
 	localStorage.setItem(LS_KEY_TAB, activeTab);
+	localStorage.setItem(LS_KEY_OPEN, String(panelOpen));
 });
 </script>