Set time zone as well when signing up

views/signup.erb

@@ -28,5 +28,10 @@
     <label for="password" class="form-label"><%= _("Password") %></label>
     <input type="password" name="password" value="<%= params[:password] %>" class="form-control">
   </div>
+  <input type="hidden" name="timezone" value="UTC">
   <button type="submit" class="btn btn-primary"><%= _("Create account") %></button>
 </form>
+
+<script>
+document.signup.timezone.value = Intl.DateTimeFormat().resolvedOptions().timeZone;
+</script>