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/api/client.ts

@@ -32,7 +32,6 @@ import type {
 	DashboardShortcutInput,
 	AlertmanagerAlertSummary,
 	AlertmanagerStatus,
-	GrafanaStatus,
 	PrometheusStatus,
 	PrometheusTarget,
 } from "../types";
@@ -299,9 +298,6 @@ export const fetchAlertmanagerAlerts = () =>
 export const fetchAlertmanagerStatus = () =>
 	get<AlertmanagerStatus>("/api/monitoring/alertmanager-status");
 
-export const fetchGrafanaStatus = () =>
-	get<GrafanaStatus>("/api/monitoring/grafana-status");
-
 export const fetchPrometheusStatus = () =>
 	get<PrometheusStatus>("/api/monitoring/prometheus-status");