chore(cleanup): 移除用户中心孤儿签到日历渲染器

credits-signin.php 已无任何引用（用户中心视图映射无 signin 项，profile-credits.php 亦不再挂载），整包删除，不保留兼容分支。

其专属 .uc-signin-calendar__title 样式与 public.css / public.min.css 产物同步移除；签到日历仍由 src/Credits/Signin.php 在签到弹窗内输出，enhancements2.js 的日历渲染逻辑保持不变。

inc/helpers/user-center-renderers/credits-signin.php

@@ -1,32 +0,0 @@
-<?php
-/**
- * User center credits: sign-in captcha + recent calendar.
- *
- * Expects extracted $context vars.
- *
- * @package AKSRT
- */
-
-defined('ABSPATH') || exit;
-
-$credits_enabled = !empty($credits_enabled);
-if (!$credits_enabled) {
-	return;
-}
-
-$signin_dates = [];
-if (class_exists('\AKSRT\Credits\Signin')) {
-	$signin_log = \AKSRT\Credits\Signin::get_instance()->get_recent_signins($user_id, 30);
-	$signin_dates = array_filter(array_map(static function ($entry) {
-		return $entry['signin_date'] ?? '';
-	}, $signin_log));
-}
-
-?>
-<div class="uc-signin-calendar" style="margin-bottom:16px;">
-	<h4 class="uc-signin-calendar__title">
-		<i class="fa fas fa-calendar" aria-hidden="true"></i>
-		<?php esc_html_e('最近 30 天签到', 'aksrt'); ?>
-	</h4>
-	<div data-aksrt-signin-calendar='<?php echo esc_attr(wp_json_encode(array_values($signin_dates))); ?>'></div>
-</div>