Fix change-password form to use direct fetch instead of authClient

authClient.changePassword does not exist in better-auth v1.6 client bundle.
Use direct POST to /api/auth/change-password endpoint instead.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/app/(student)/profile/change-password-form.tsx

@@ -1,7 +1,6 @@
 "use client";
 
 import { useState } from "react";
-import { authClient } from "@/lib/auth-client";
 
 const inputStyle: React.CSSProperties = {
   border: "2px solid var(--border)",
@@ -33,14 +32,14 @@ export function ChangePasswordForm() {
     }
 
     setLoading(true);
-    const result = await authClient.changePassword({
-      currentPassword: current,
-      newPassword: next,
-      revokeOtherSessions: false,
+    const res = await fetch("/api/auth/change-password", {
+      method: "POST",
+      headers: { "Content-Type": "application/json" },
+      body: JSON.stringify({ currentPassword: current, newPassword: next, revokeOtherSessions: false }),
     });
     setLoading(false);
 
-    if (result.error) {
+    if (!res.ok) {
       setError("Неверный текущий пароль");
       return;
     }