feat(prometheus-direct-charting): slice 1 — prom range query + chart rebrand

Add PrometheusWidgetSource._fetch_chart hitting /api/v1/query_range directly
(SC-101..104). New shared helpers in widgets/prometheus_range.py:
step_for_window (window preset -> step, ~200pts) and normalize_prometheus_matrix
(extracted label/dedup rule, retargeted at Prom matrix, robust to malformed
data). Chart widget kind moved grafana->prometheus in both registries;
GrafanaChartWidget renamed -> PrometheusChartWidget (git mv, recharts body
preserved). Grafana binding/service untouched (removed in slice 3).

Backend: 298 pytest pass, ruff clean. Frontend: 128 vitest pass, build+lint green.

frontend/src/integrations/registry.ts

@@ -2,7 +2,7 @@ import type { ComponentType } from "react";
 import { AlertmanagerAlertsWidget } from "../widgets/AlertmanagerAlertsWidget";
 import { BackupsWidget } from "../widgets/BackupsWidget";
 import { GrafanaLinkWidget } from "../widgets/GrafanaLinkWidget";
-import { GrafanaChartWidget } from "../widgets/GrafanaChartWidget";
+import { PrometheusChartWidget } from "../widgets/PrometheusChartWidget";
 import { JellyfinWidget } from "../widgets/JellyfinWidget";
 import { JellyfinNowPlayingWidget } from "../widgets/JellyfinNowPlayingWidget";
 import { PrometheusMetricWidget } from "../widgets/PrometheusMetricWidget";
@@ -88,39 +88,6 @@ export const SERVICE_REGISTRY: Record<string, ServiceBinding> = {
 				},
 				component: GrafanaLinkWidget,
 			},
-			{
-				kind: "chart",
-				name: "Chart",
-				description: "Live time-series chart from a Grafana datasource query.",
-				refreshIntervalMs: 60_000,
-				defaultConfig: {
-					datasource_uid: "prometheus",
-					query: "",
-					from_ts: "now-1h",
-					to_ts: "now",
-					interval_ms: 30_000,
-					max_data_points: 100,
-				},
-				configSchema: {
-					type: "object",
-					properties: {
-						datasource_uid: {
-							type: "string",
-							description: "Grafana datasource UID (e.g. 'prometheus')",
-						},
-						query: {
-							type: "string",
-							description: "Query expression (e.g. PromQL)",
-						},
-						from_ts: { type: "string" },
-						to_ts: { type: "string" },
-						interval_ms: { type: "integer" },
-						max_data_points: { type: "integer" },
-					},
-					required: ["query"],
-				},
-				component: GrafanaChartWidget,
-			},
 		],
 	},
 	prometheus: {
@@ -141,6 +108,28 @@ export const SERVICE_REGISTRY: Record<string, ServiceBinding> = {
 				},
 				component: PrometheusMetricWidget,
 			},
+			{
+				kind: "chart",
+				name: "Chart",
+				description: "Multi-series line chart from a PromQL range query.",
+				refreshIntervalMs: 60_000,
+				defaultConfig: { promql: "", window: "1h" },
+				configSchema: {
+					type: "object",
+					properties: {
+						promql: {
+							type: "string",
+							description: "PromQL range query expression",
+						},
+						window: {
+							type: "string",
+							description: "Time window preset (1h, 6h, 24h, 7d)",
+						},
+					},
+					required: ["promql"],
+				},
+				component: PrometheusChartWidget,
+			},
 		],
 	},
 	jellyfin: {