feat(housekeeping): add per-hotel theme manager with import/export and background

Theme Manager under /admin-next/hotel/theme-manager lets the owner save, apply, rename, delete, import, and export custom themes, plus set a custom site background by URL or upload. Themes are stored in WebsiteSetting/custom_themes JSON so they survive CMS updates.

src/app/admin-next/hotel/theme-manager/page.tsx

@@ -0,0 +1,47 @@
+import { getTranslations } from "next-intl/server";
+import { getThemeManagerData } from "@/actions/theme-manager";
+import { ThemeManagerPanel } from "@/components/admin/theme/theme-manager-panel";
+import { HousekeepingPageShell } from "@/features/housekeeping/foundation/page/housekeeping-page-shell";
+
+const MESSAGE_PREFIX = "pages.housekeeping.domains.hotel.routes.themeManager";
+
+const NOTICES = new Set([
+	"saved",
+	"applied",
+	"renamed",
+	"deleted",
+	"imported",
+	"preset",
+	"background",
+	"importError",
+	"backgroundError",
+]);
+
+export default async function HousekeepingHotelThemeManagerPage({
+	searchParams,
+}: {
+	searchParams: Promise<{ [key: string]: string | string[] | undefined }>;
+}) {
+	const t = await getTranslations(MESSAGE_PREFIX);
+	const params = await searchParams;
+	const first = Array.isArray(params.notice) ? params.notice[0] : params.notice;
+	const notice = first && NOTICES.has(first) ? first : undefined;
+
+	const { themes, current, background } = await getThemeManagerData();
+	const activeName =
+		typeof current.theme_preset === "string" && current.theme_preset
+			? current.theme_preset
+			: "Atom (golden)";
+
+	return (
+		<HousekeepingPageShell title={t("title")} description={t("description")}>
+			<ThemeManagerPanel
+				themes={themes}
+				current={current}
+				background={background}
+				activeName={activeName}
+				notice={notice}
+			/>
+		</HousekeepingPageShell>
+	);
+}