appview/pages: fix checkbox name for notifications when mentioned #847

Before: when you save notifications preferences, "when someone mentions you" always gets deselected as the HTML checkbox is named mentioned but the form processing logic checks for user_mentioned

          <input type="checkbox" name="mentioned" {{if .Preferences.UserMentioned}}checked{{end}}>
UserMentioned:      r.FormValue("user_mentioned") == "on",

After: HTML checkbox is renamed to user_mentioned so preference is saved correctly

Changed files
+1 -1
appview
pages
templates
user
+1 -1
appview/pages/templates/user/settings/notifications.html
···
</div>
</div>
<label class="flex items-center gap-2">
-
<input type="checkbox" name="mentioned" {{if .Preferences.UserMentioned}}checked{{end}}>
+
<input type="checkbox" name="user_mentioned" {{if .Preferences.UserMentioned}}checked{{end}}>
</label>
</div>