feat(panel): add sponsor slots fed from sponsors.sanaei.dev

Monthly sponsor placements need to change without cutting a panel
release. Panels now read 3X/sponsors.json from the MHSanaei/sponsors
repo (GitHub Pages on sponsors.sanaei.dev) and show active sponsors in
four slots: an overview banner, a rotating sidebar card (max three), the
login page and a new Sponsors page that also lists open placements.

An entry shows only while enable is not false and until is in the
future; links must be https and logos are png/webp/jpg by name only.
The list is cached for an hour and the last good copy survives upstream
failures; logos are proxied through /sponsors/logo/:name with failures
cached, so CSP stays 'self' and admin browsers never reach a third
party. Admins can hide a slot for 24h. Under XUI_DEBUG the panel reads
a sibling ../sponsors/3X checkout so edits can be previewed before push.

frontend/src/pages/index/IndexPage.tsx

@@ -22,6 +22,7 @@ import { useStatusQuery } from '@/api/queries/useStatusQuery';
 import { useMediaQuery } from '@/hooks/useMediaQuery';
 import AppSidebar from '@/layouts/AppSidebar';
 import { LazyMount } from '@/components/utility';
+import SponsorSlot from '@/components/sponsor/SponsorSlot';
 import { setMessageInstance } from '@/utils/messageBus';
 import OverviewActionBar from './OverviewActionBar';
 import VitalTile from './VitalTile';
@@ -213,6 +214,8 @@ export default function IndexPage() {
                     onOpenVersionSwitch={() => setVersionOpen(true)}
                   />
 
+                  <SponsorSlot slot="dashboard" />
+
                   {health && (
                     <div className="ov-health" style={{ color: health.color }}>
                       <span className="ov-health-mark" />