feat(admin): Server Action'larla kullanıcı yönetimi ve gerçek oturumlu sayfalar

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/features/admin-users/guards.ts

@@ -35,18 +35,3 @@ export function checkAdminAction(action: AdminAction, ctx: GuardContext): GuardV
   if (removesAdmin && ctx.adminCount <= 1) return "lastAdmin";
   return null;
 }
-
-/** Kullanıcı adı / e-posta benzersizlik kontrolü (normalize edilmiş değerlerle). */
-export function findUniqueConflicts(
-  users: ReadonlyArray<{ id: string; username: string; email?: string }>,
-  values: { username: string; email?: string },
-  excludeId?: string,
-): { username?: "taken"; email?: "taken" } {
-  const others = users.filter((u) => u.id !== excludeId);
-  return {
-    ...(others.some((u) => u.username === values.username) ? { username: "taken" as const } : {}),
-    ...(values.email && others.some((u) => u.email === values.email)
-      ? { email: "taken" as const }
-      : {}),
-  };
-}