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/help-tickets.ts

@@ -22,10 +22,10 @@ export async function createTicket(formData: FormData): Promise<void> {
   if (!(await rateLimit(`ticket:${userId}`, 3, 60_000)).ok) return;
 
   const raw = {
-    title: String(formData.get("title") ?? "")
+    title: String(formData.get("title") ?? "").normalize("NFC")
       .trim()
       .slice(0, 255),
-    content: String(formData.get("content") ?? "")
+    content: String(formData.get("content") ?? "").normalize("NFC")
       .trim()
       .slice(0, 5000),
   };