Service IA refinement: nav naming, instance tabs, config to Settings, configurable Overview

Four coupled changes to the services-as-hub IA:

1. Nav entries use service TYPE names (Jellyfin, SSH Tasks, Alertmanager,
   Grafana, Prometheus, Backups, Authentik) instead of conceptual names
   (Media, Files, Actions, Alerts, Users). ssh_tasks collapses to one
   entry ('SSH Tasks') instead of two. The content tabs inside each
   service page surface the concepts (Files, Actions).

2. Service page gains a two-level tab structure when multiple enabled
   instances of the same type exist: instance tabs on top ([Main Jellyfin]
   [Backup Jellyfin]), content tabs below ([Overview] [Media] [Requests]
   [Widgets]). Clicking an instance tab navigates to the sibling's route.
   Single instance: no instance tabs. Replaces the dropdown switcher.

3. Config tab (connection fields, secrets, enable/disable, delete) moves
   from the service page to Settings > Services tab. The service page
   becomes a PURE operational view (Overview + content tabs + Widgets) --
   no save/delete/config state. Settings gains a 4th tab 'Services' with
   ServiceConfigEditor per instance (schema-driven config fields, secrets
   with leave-blank-to-keep semantics, ConfirmDialog on delete).

4. Overview tab is now a configurable widget grid per service instance.
   Each instance manages its own set of widgets on its Overview. Backend
   widget list endpoints gain ?service_id= and ?scope= (dashboard|service)
   filter params; the main Dashboard uses scope=dashboard to exclude
   service-scoped widgets. The OverviewTab reuses WidgetInstanceCard +
   WidgetConfigDialog. Empty state CTA for instances with no widgets.

All service-tab stubs are replaced; stubs.tsx deleted.

272 backend tests pass (+1 widget filter); 121 frontend tests pass (+3
instance-tabs + OverviewTab); lint/build green both sides.

frontend/src/pages/service-tabs/OverviewTab.tsx

@@ -0,0 +1,78 @@
+/**
+ * Configurable per-service Overview tab.
+ *
+ * Each service instance manages its own set of widgets on this tab. The
+ * widget system is reused from the main Dashboard: widget instances with
+ * a `service_id` matching this instance are fetched and rendered in a
+ * responsive grid. An edit button opens the WidgetConfigDialog (same one
+ * the Dashboard uses) for add/remove/reorder/enable/disable.
+ */
+import { useMemo, useState } from "react";
+import { Alert, AlertDescription } from "@/components/ui/alert";
+import { Button } from "@/components/ui/button";
+import { Settings2 } from "lucide-react";
+import { useWidgetInstances } from "../../hooks/useWidgets";
+import { WidgetInstanceCard } from "../../components/WidgetInstance";
+import { WidgetConfigDialog } from "../../components/WidgetConfigDialog";
+import type { ServiceInstance } from "../../types";
+
+export function OverviewTab({ instance }: { instance: ServiceInstance }) {
+	const { data: widgets = [] } = useWidgetInstances(instance.id);
+	const [configOpen, setConfigOpen] = useState(false);
+
+	const visibleWidgets = useMemo(
+		() =>
+			widgets
+				.filter((w) => w.enabled)
+				.sort((a, b) => a.sort_order - b.sort_order),
+		[widgets],
+	);
+
+	return (
+		<div className="flex flex-col gap-4">
+			<div className="flex items-center justify-between">
+				<h3 className="text-sm font-semibold text-muted-foreground">
+					{instance.name} overview
+				</h3>
+				<Button
+					variant="outline"
+					size="sm"
+					className="mobile-touch-target"
+					onClick={() => setConfigOpen(true)}
+				>
+					<Settings2 className="size-4" />
+					Edit widgets
+				</Button>
+			</div>
+
+			{visibleWidgets.length > 0 ? (
+				<div className="grid grid-cols-1 gap-4 md:grid-cols-2">
+					{visibleWidgets.map((widget) => (
+						<WidgetInstanceCard key={widget.id} widget={widget} />
+					))}
+				</div>
+			) : (
+				<Alert>
+					<AlertDescription className="flex flex-col gap-3">
+						<span>
+							No widgets on this overview yet. Add widgets to show key metrics
+							and information for {instance.name}.
+						</span>
+						<Button
+							size="sm"
+							className="w-fit mobile-touch-target"
+							onClick={() => setConfigOpen(true)}
+						>
+							Add widgets
+						</Button>
+					</AlertDescription>
+				</Alert>
+			)}
+
+			<WidgetConfigDialog
+				open={configOpen}
+				onClose={() => setConfigOpen(false)}
+			/>
+		</div>
+	);
+}