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/hooks/usePageTitle.ts

@@ -14,6 +14,7 @@ const TITLE_KEYS: Record<string, string> = {
   '/outbound': 'menu.outbounds',
   '/routing': 'menu.routing',
   '/api-docs': 'menu.apiDocs',
+  '/sponsors': 'menu.sponsors',
 };
 
 export function usePageTitle() {