feat(prometheus-direct-charting): slice 3 — remove grafana + config rewrite + changelog

Remove the entire Grafana surface: integrations/grafana.py, GrafanaWidgetSource
(+ _fetch_chart, now redundant since prometheus chart exists), GrafanaLinkWidget,
LinksTab, get_grafana_status endpoint, useGrafanaStatus hook, GrafanaStatus type,
fetchGrafanaStatus client fn, registry/nav/tab entries (FE+BE). Rewrite
config.yaml thin-dashboard rule to match reality (recharts is sanctioned for
Prometheus-backed series). CHANGELOG migration note added.

Backend: 293 pytest pass, ruff clean. Frontend: build+lint green (0 errors).
SC-115/116 grep-clean (only prometheus_range.py migration comments + Dashboard.test
shortcut fixture remain — both spec-allowed).

frontend/src/integrations/registry.ts

@@ -1,7 +1,6 @@
 import type { ComponentType } from "react";
 import { AlertmanagerAlertsWidget } from "../widgets/AlertmanagerAlertsWidget";
 import { BackupsWidget } from "../widgets/BackupsWidget";
-import { GrafanaLinkWidget } from "../widgets/GrafanaLinkWidget";
 import { PrometheusChartWidget } from "../widgets/PrometheusChartWidget";
 import { PrometheusGaugeWidget } from "../widgets/PrometheusGaugeWidget";
 import { PrometheusMeanWidget } from "../widgets/PrometheusMeanWidget";
@@ -69,29 +68,6 @@ export const SERVICE_REGISTRY: Record<string, ServiceBinding> = {
 			},
 		],
 	},
-	grafana: {
-		serviceType: "grafana",
-		name: "Grafana",
-		description: "Dashboards, metrics, and logs.",
-		widgets: [
-			{
-				kind: "link",
-				name: "Dashboard link",
-				description: "Deep-link to a Grafana dashboard or panel.",
-				refreshIntervalMs: 0,
-				defaultConfig: { dashboard_uid: "" },
-				configSchema: {
-					type: "object",
-					properties: {
-						dashboard_uid: { type: "string" },
-						panel_id: { type: "integer" },
-					},
-					required: ["dashboard_uid"],
-				},
-				component: GrafanaLinkWidget,
-			},
-		],
-	},
 	prometheus: {
 		serviceType: "prometheus",
 		name: "Prometheus",