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/vite.config.js

@@ -6,13 +6,13 @@ export default defineConfig({
 	server: {
 		proxy: {
 			'/api': {
-				target: 'http://127.0.0.1:8101',
+				target: process.env.BACKEND_URL || 'http://127.0.0.1:8000',
 				changeOrigin: true,
 				secure: false,
 				rewrite: (path) => path.replace(/^\/api/, '/api')
 			},
 			'/ws': {
-				target: 'ws://127.0.0.1:8101',
+				target: (process.env.BACKEND_URL || 'http://127.0.0.1:8000').replace(/^http/, 'ws'),
 				ws: true,
 				changeOrigin: true,
 				secure: false