fix(observability): add grafana healthcheck and service_healthy depends_on

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

docker-compose.observability.yml

@@ -149,10 +149,19 @@ services:
     volumes:
       - grafana_data:/var/lib/grafana
       - ./infra/observability/grafana/provisioning:/etc/grafana/provisioning:ro
+    healthcheck:
+      test: ["CMD-SHELL", "wget -qO- http://localhost:3000/api/health | grep -q ok || exit 1"]
+      interval: 30s
+      timeout: 5s
+      retries: 3
+      start_period: 30s
     depends_on:
-      - prometheus
-      - loki
-      - tempo
+      prometheus:
+        condition: service_healthy
+      loki:
+        condition: service_healthy
+      tempo:
+        condition: service_healthy
     networks:
       - obs-net