Add custom domain support for published status pages.

Fixes #3647

server/src/utils/statusPageDomain.ts

@@ -0,0 +1,29 @@
+export const normalizeStatusPageDomain = (value?: string | null): string | null => {
+	if (typeof value !== "string") {
+		return null;
+	}
+
+	const trimmed = value.trim().toLowerCase();
+	if (!trimmed) {
+		return null;
+	}
+
+	// Strip scheme, path, and port if a full URL was pasted.
+	const withoutScheme = trimmed.replace(/^https?:\/\//, "");
+	const hostname = withoutScheme.split("/")[0]?.split(":")[0] ?? "";
+
+	return hostname || null;
+};
+
+export const resolveStatusPageDomainFromRequest = (hostHeader?: string | null, queryDomain?: string | null): string | null => {
+	const fromQuery = normalizeStatusPageDomain(queryDomain);
+	if (fromQuery) {
+		return fromQuery;
+	}
+
+	if (!hostHeader) {
+		return null;
+	}
+
+	return normalizeStatusPageDomain(hostHeader.split(":")[0]);
+};