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.

tools/openapigen/main.go

@@ -112,7 +112,7 @@ func run(root, outDir string) error {
 		},
 		{
 			Path:        resolveRel(root, "internal/web/service/panel"),
-			StructAllow: setOf("ApiTokenView", "PanelUpdateStatus"),
+			StructAllow: setOf("ApiTokenView", "PanelUpdateStatus", "Sponsor", "SponsorList"),
 		},
 		{
 			Path:        resolveRel(root, "internal/amneziawg"),