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/radio-apply.ts

@@ -11,7 +11,7 @@ const TEXT_MAX = 5000;
 const STYLE_MAX = 5000;
 
 function str(form: FormData, key: string, max: number): string {
-  return String(form.get(key) ?? "")
+  return String(form.get(key) ?? "").normalize("NFC")
     .trim()
     .slice(0, max);
 }