feat(grafana-metric-gateway): slice 2 — rename widgets to Metric*

git mv PrometheusChartWidget→MetricChartWidget, PrometheusGaugeWidget→
MetricGaugeWidget, PrometheusMeanWidget→MetricMeanWidget (+ 3 test files,
R100 history preserved). Update registry imports/refs + barrel exports.
Adapt PrometheusMetricWidget for §3.4 Option A: read normalized {result:
[{label,points}]} series shape (last-point extraction) instead of old Prom
{resultType,result} vector. PrometheusMetricWidget NOT renamed (design §3.1).
GM-111/112/116 satisfied. All gates: 151 vitest, build exit 0, lint 0 errors.

frontend/src/integrations/registry.ts

@@ -1,9 +1,9 @@
 import type { ComponentType } from "react";
 import { AlertmanagerAlertsWidget } from "../widgets/AlertmanagerAlertsWidget";
 import { BackupsWidget } from "../widgets/BackupsWidget";
-import { PrometheusChartWidget } from "../widgets/PrometheusChartWidget";
-import { PrometheusGaugeWidget } from "../widgets/PrometheusGaugeWidget";
-import { PrometheusMeanWidget } from "../widgets/PrometheusMeanWidget";
+import { MetricChartWidget } from "../widgets/MetricChartWidget";
+import { MetricGaugeWidget } from "../widgets/MetricGaugeWidget";
+import { MetricMeanWidget } from "../widgets/MetricMeanWidget";
 import { JellyfinWidget } from "../widgets/JellyfinWidget";
 import { JellyfinNowPlayingWidget } from "../widgets/JellyfinNowPlayingWidget";
 import { PrometheusMetricWidget } from "../widgets/PrometheusMetricWidget";
@@ -109,7 +109,7 @@ export const SERVICE_REGISTRY: Record<string, ServiceBinding> = {
 					},
 					required: ["promql"],
 				},
-				component: PrometheusChartWidget,
+				component: MetricChartWidget,
 			},
 			{
 				kind: "gauge",
@@ -133,7 +133,7 @@ export const SERVICE_REGISTRY: Record<string, ServiceBinding> = {
 					},
 					required: ["promql"],
 				},
-				component: PrometheusGaugeWidget,
+				component: MetricGaugeWidget,
 			},
 			{
 				kind: "mean",
@@ -156,7 +156,7 @@ export const SERVICE_REGISTRY: Record<string, ServiceBinding> = {
 					},
 					required: ["promql"],
 				},
-				component: PrometheusMeanWidget,
+				component: MetricMeanWidget,
 			},
 		],
 	},