fix(maintenance): auto-expiry + adaptive markdown height + tests

- Auto-expiry: expired events auto-end on GET /events via task manager
- Height: _estimate_markdown_height adapted to unit=8px scale with padding detection
- CRITICAL-1: removed dead import remove_chart_from_position (QA finding)
- CRITICAL-2: added chart alive check in ensure_banner_chart (QA finding)
- CRITICAL-3: fixed test assertions update_markdown_chart → update_banner_on_dashboard
- @POST contract: fixed return range [2,12] → [19,200]
- Tests: 8 new tests (auto-expiry + layout height)

frontend/e2e/fixtures/global-setup.js

@@ -11,13 +11,16 @@ const FRONTEND_URL = process.env.FRONTEND_URL || 'http://127.0.0.1:8102';
 async function globalSetup() {
 	console.log(`[E2E] Pre-flight check — Backend: ${BACKEND_URL}, Frontend: ${FRONTEND_URL}`);
 
-	// 1. Check backend health
+	// 1. Check backend health (accept 401/403 as "server is alive but needs auth")
 	try {
 		const healthRes = await fetch(`${BACKEND_URL}/api/health/summary`);
-		if (!healthRes.ok) {
+		if (healthRes.ok) {
+			console.log('[E2E] Backend is healthy ✅');
+		} else if (healthRes.status === 401 || healthRes.status === 403) {
+			console.log(`[E2E] Backend is alive (HTTP ${healthRes.status} — auth required) ✅`);
+		} else {
 			throw new Error(`Backend health check failed: ${healthRes.status}`);
 		}
-		console.log('[E2E] Backend is healthy ✅');
 	} catch (err) {
 		console.error(`[E2E] Backend unreachable: ${err.message}`);
 		console.error('[E2E] Make sure the stack is running: docker compose up -d');