BAI-3: harden live readiness diagnostics

Co-authored-by: multica-agent <github@multica.ai>

app/backend/application.py

@@ -43,6 +43,7 @@ from backend.features.screener.service import (
 from backend.features.sentiment import SentimentServiceMixin
 from backend.features.sentiment.routes import SentimentRoutesMixin
 from backend.features.system import SystemHttpMixin
+from backend.features.system.health import HealthServiceMixin
 from backend.features.system.routes import SystemRoutesMixin
 from backend.features.system.service import SystemServiceMixin
 from backend.features.themes import ThemeServiceMixin
@@ -77,6 +78,7 @@ LEGACY_SECRET_KEYS = {
 
 
 class DashboardService(
+    HealthServiceMixin,
     SystemServiceMixin,
     AccountApplicationMixin,
     JobServiceMixin,