Reapply "Add missing admin action files and navigation links"

This reverts commit 4d515bc400.

src/actions/radio-shouts.ts

@@ -28,7 +28,9 @@ export async function postShout(formData: FormData): Promise<void> {
   if (!(await rateLimit(`shout:${userId}`, 5, 30_000)).ok) return;
 
   const raw = {
-    message: String(formData.get("message") ?? "").trim().slice(0, 255),
+    message: String(formData.get("message") ?? "")
+      .trim()
+      .slice(0, 255),
   };
 
   const parsed = shoutSchema.safeParse(raw);