Add Jellyfin Now Playing + Grafana Panel embed widgets

Two new additive widget kinds:

Jellyfin 'now_playing': like the existing 'activity' widget but filters
to only sessions with active playback (NowPlayingItem present + not
paused). Shows who's actually watching right now. The 'activity' kind
is unchanged (shows all sessions including idle).

Grafana 'panel': embeds a single Grafana panel directly in the app via
an iframe, using Grafana's /d-solo/ endpoint (renders one panel without
dashboard chrome, kiosk=tv). Configurable dashboard_uid, panel_id, and
time range (from/to, defaults now-1h/now). Includes a fallback 'Open in
Grafana' link for when embedding is blocked by X-Frame-Options/CSP. The
'link' kind is unchanged (still builds a deep-link URL).

Backend: new widget configs + definitions on jellyfin/grafana; source
adapter logic (session filter for now_playing; d-solo embed URL for
panel); 6 new tests.

Frontend: JellyfinNowPlayingWidget + GrafanaPanelWidget components;
registry bindings; 6 new tests.

278 backend tests pass (+6); 127 frontend tests pass (+6); lint/build
green both sides.

frontend/src/integrations/registry.ts

@@ -2,7 +2,9 @@ import type { ComponentType } from "react";
 import { AlertmanagerAlertsWidget } from "../widgets/AlertmanagerAlertsWidget";
 import { BackupsWidget } from "../widgets/BackupsWidget";
 import { GrafanaLinkWidget } from "../widgets/GrafanaLinkWidget";
+import { GrafanaPanelWidget } from "../widgets/GrafanaPanelWidget";
 import { JellyfinWidget } from "../widgets/JellyfinWidget";
+import { JellyfinNowPlayingWidget } from "../widgets/JellyfinNowPlayingWidget";
 import { PrometheusMetricWidget } from "../widgets/PrometheusMetricWidget";
 import { SshTaskWidget } from "../widgets/SshTaskWidget";
 import { StaticWidget } from "../widgets/StaticWidget";
@@ -86,6 +88,29 @@ export const SERVICE_REGISTRY: Record<string, ServiceBinding> = {
 				},
 				component: GrafanaLinkWidget,
 			},
+			{
+				kind: "panel",
+				name: "Panel embed",
+				description: "Embed a Grafana panel directly.",
+				refreshIntervalMs: 0,
+				defaultConfig: {
+					dashboard_uid: "",
+					panel_id: 1,
+					from_ts: "now-1h",
+					to_ts: "now",
+				},
+				configSchema: {
+					type: "object",
+					properties: {
+						dashboard_uid: { type: "string" },
+						panel_id: { type: "integer" },
+						from_ts: { type: "string" },
+						to_ts: { type: "string" },
+					},
+					required: ["dashboard_uid", "panel_id"],
+				},
+				component: GrafanaPanelWidget,
+			},
 		],
 	},
 	prometheus: {
@@ -122,6 +147,15 @@ export const SERVICE_REGISTRY: Record<string, ServiceBinding> = {
 				configSchema: { type: "object", properties: {}, required: [] },
 				component: JellyfinWidget,
 			},
+			{
+				kind: "now_playing",
+				name: "Now Playing",
+				description: "Only sessions actively playing media.",
+				refreshIntervalMs: 30_000,
+				defaultConfig: {},
+				configSchema: { type: "object", properties: {}, required: [] },
+				component: JellyfinNowPlayingWidget,
+			},
 		],
 	},
 	nextcloud: {