cron: separate webhook POST delivery from announce (#17901)

* cron: split webhook delivery from announce mode

* cron: validate webhook delivery target

* cron: remove legacy webhook fallback config

* fix: finalize cron webhook delivery prep (#17901) (thanks @advaitpaliwal)

---------

Co-authored-by: Tyler Yust <TYTYYUST@YAHOO.COM>

src/cron/webhook-url.ts

@@ -0,0 +1,22 @@
+function isAllowedWebhookProtocol(protocol: string) {
+  return protocol === "http:" || protocol === "https:";
+}
+
+export function normalizeHttpWebhookUrl(value: unknown): string | null {
+  if (typeof value !== "string") {
+    return null;
+  }
+  const trimmed = value.trim();
+  if (!trimmed) {
+    return null;
+  }
+  try {
+    const parsed = new URL(trimmed);
+    if (!isAllowedWebhookProtocol(parsed.protocol)) {
+      return null;
+    }
+    return trimmed;
+  } catch {
+    return null;
+  }
+}