Add NFC normalization to all FormData inputs across 41 server actions

All user-supplied string values from FormData now go through
String.prototype.normalize('NFC') to prevent Unicode homoglyph
attacks and canonicalization bypasses. NFC is idempotent for
already-normalized strings, so this is a pure security improvement
with zero behavioral change for legitimate users.

src/actions/admin-alerts.ts

@@ -13,7 +13,7 @@ import { rcon } from "@/lib/services/rcon";
 export async function sendHotelAlert(formData: FormData): Promise<void> {
   await requireStaff();
 
-  const message = String(formData.get("message") ?? "")
+  const message = String(formData.get("message") ?? "").normalize("NFC")
     .trim()
     .slice(0, 1000);
   if (!message) return;