feat(dashboard): Classic Split — 2-col layout, remove DashboardMentions widget

Restructures the dashboard to a lg:grid-cols-[1fr_300px] split:
- Left column: DashboardRecentDocuments (with stats footnote)
- Right column: DropZone (canWrite) + DashboardNeedsMetadata (flex-1)

Adds showRightColumn guard (canWrite || incompleteDocs.length > 0) so
read-only users with a complete archive never see an empty 300px ghost
column. DashboardMentions is removed from the page; the file is kept.

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

frontend/src/routes/page.svelte.spec.ts

@@ -21,8 +21,12 @@ const emptyData = {
 	user: undefined,
 	canWrite: true,
 	canAnnotate: false,
+	isDashboard: false,
 	filters: { q: '', from: '', to: '', senderId: '', receiverId: '', tags: [] },
 	documents: [],
+	incompleteDocs: [],
+	recentDocs: [],
+	stats: null,
 	incompleteCount: 0,
 	initialValues: { senderName: '', receiverName: '' },
 	error: null
@@ -189,6 +193,42 @@ describe('Home page – search input keystroke preservation', () => {
 	});
 });
 
+// ─── Dashboard mode ───────────────────────────────────────────────────────────
+
+describe('Home page – dashboard mode', () => {
+	const dashboardData = {
+		...emptyData,
+		isDashboard: true,
+		canWrite: false,
+		incompleteDocs: [],
+		recentDocs: []
+	};
+
+	it('hides the right column when canWrite is false and incompleteDocs is empty', async () => {
+		render(Page, { data: dashboardData });
+		const rightCol = page.getByTestId('dashboard-right-column');
+		await expect.element(rightCol).not.toBeInTheDocument();
+	});
+
+	it('shows the right column when canWrite is true', async () => {
+		render(Page, { data: { ...dashboardData, canWrite: true } });
+		const rightCol = page.getByTestId('dashboard-right-column');
+		await expect.element(rightCol).toBeInTheDocument();
+	});
+
+	it('shows the right column when incompleteDocs is non-empty', async () => {
+		render(Page, {
+			data: {
+				...dashboardData,
+				canWrite: false,
+				incompleteDocs: [{ id: 'd1', title: 'Taufschein' }]
+			}
+		});
+		const rightCol = page.getByTestId('dashboard-right-column');
+		await expect.element(rightCol).toBeInTheDocument();
+	});
+});
+
 // ─── Error state ──────────────────────────────────────────────────────────────
 
 describe('Home page – error state', () => {