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)

docker-compose.e2e.yml

@@ -47,8 +47,7 @@ services:
     ports:
       - "${BACKEND_HOST_PORT:-8103}:8000"
     volumes:
-      - ./config.json:/app/config.json:ro
-      - e2e_storage:/home/busya/dev/ss-tools-storage
+      - e2e_storage:/app/storage
 
   # Playwright runner (CI mode)
   e2e-runner: