fix(dashboard): empty state for comments and messages tabs

These tabs have no backend endpoint yet (only per-doctor comments and
admin exist; user messages don't), so they read the always-empty
user.comments/user.messages. Guard against null and show a clear empty
state instead of a blank list.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

components/dashboard/userAccount/sidebars/comments/index.js

@@ -1,15 +1,25 @@
 import Comment from "./Comment";
 
 function Comments({ user, loading }) {
+  const comments = user?.comments ?? [];
+
+  if (comments.length === 0) {
+    return (
+      <p className="text-[#7E7E7E] opacity-page text-[14px] md:text-[16px] font-medium text-center py-[56px]">
+        نظری ثبت نکرده‌اید.
+      </p>
+    );
+  }
+
   return (
     <ul className="flex opacity-page flex-col items-start justify-start gap-[24px] md:gap-[22px] lg:gap-[20px]">
-      {user.comments.map((item, idx) => (
+      {comments.map((item, idx) => (
         <Comment
           key={idx}
           idx={idx}
           data={item}
           loading={loading}
-          length={user.comments.length}
+          length={comments.length}
         />
       ))}
     </ul>

components/dashboard/userAccount/sidebars/messages/index.js

@@ -1,15 +1,25 @@
 import Message from "./Message";
 
 function Messages({ user, loading }) {
+  const messages = user?.messages ?? [];
+
+  if (messages.length === 0) {
+    return (
+      <p className="text-[#7E7E7E] opacity-page text-[14px] md:text-[16px] font-medium text-center py-[56px]">
+        پیامی ندارید.
+      </p>
+    );
+  }
+
   return (
     <ul className="flex opacity-page flex-col gap-[24px] md:gap-[20px] lg:gap-[16px]">
-      {user.messages.map((item, idx) => (
+      {messages.map((item, idx) => (
         <Message
           key={idx}
           idx={idx}
           data={item}
           loading={loading}
-          length={user.messages.length}
+          length={messages.length}
         />
       ))}
     </ul>