feat(network): add session status card

Display server health metrics from the unused /session endpoint:
- Connected clients count (live from useClientStore)
- Server uptime since last restart
- Last client connection time (relative)
- Last integration request time (relative)
- Server timezone
- Cloud latency (Docker only) with warning threshold

Adds useSessionStats hook with 60s refetch interval, new NetworkStatus
component as first card in Network panel, and navigation menu entries
for Server status and Network interfaces sections.

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01NrhcEgY8mqaxZi8veMPrrx

apps/client/src/common/hooks-query/useSessionStats.ts

@@ -0,0 +1,17 @@
+import { useQuery } from '@tanstack/react-query';
+import { SessionStats } from 'ontime-types';
+
+import { queryRefetchInterval } from '../../ontimeConfig';
+import { SESSION_STATS } from '../api/constants';
+import { getSessionStats } from '../api/session';
+
+export default function useSessionStats() {
+  const { data, status, isError, refetch } = useQuery<SessionStats>({
+    queryKey: SESSION_STATS,
+    queryFn: ({ signal }) => getSessionStats({ signal }),
+    placeholderData: (previousData, _previousQuery) => previousData,
+    refetchInterval: queryRefetchInterval,
+  });
+
+  return { data, status, isError, refetch };
+}