修复了一些问题

src/Settings/AuthReader.php

@@ -86,7 +86,7 @@ trait AuthReader {
             $theme_mode = 'no';
         }
         return [
-            'background'   => self::get_value('sign_page_background', []),
+            'background'   => self::auth_gallery_ids('sign_page_background'),
             'theme_mode'   => $theme_mode,
             'show_header'  => (bool) self::get_value('sign_show_header', true),
             'card_position' => in_array((string) self::get_value('sign_card_position', 'right'), ['left', 'center', 'right'], true)
@@ -99,16 +99,27 @@ trait AuthReader {
     /** 弹窗 UI 配置数组 */
     public static function modal_ui(): array {
         return [
-            'background' => self::get_value('sign_modal_background', []),
+            'background' => self::auth_gallery_ids('sign_modal_background'),
             'show_logo'  => (bool) self::get_value('sign_modal_show_logo', false),
         ];
     }
 
+	/** 认证图片库的唯一存储格式：正整数附件 ID 数组。 */
+	private static function auth_gallery_ids(string $key): array {
+		$value = self::get_value($key, []);
+		if (!is_array($value)) {
+			return [];
+		}
+
+		$ids = array_values(array_filter(array_map('absint', $value)));
+		return array_values(array_unique($ids));
+	}
+
     /** 登录框日间 LOGO URL（空时回退全局 logo_url） */
     public static function user_logo_url(): string {
-        $ids = self::get_value('user_logo', []);
-        if (is_array($ids) && !empty($ids)) {
-            $url = wp_get_attachment_url((int) $ids[0]);
+        $ids = self::auth_gallery_ids('user_logo');
+        if ($ids) {
+            $url = wp_get_attachment_image_url($ids[0], 'full');
             if ($url) return $url;
         }
         return self::logo_url();
@@ -116,9 +127,9 @@ trait AuthReader {
 
     /** 登录框夜间 LOGO URL（空时回退全局 logo_dark_url） */
     public static function user_logo_dark_url(): string {
-        $ids = self::get_value('user_logo_dark', []);
-        if (is_array($ids) && !empty($ids)) {
-            $url = wp_get_attachment_url((int) $ids[0]);
+        $ids = self::auth_gallery_ids('user_logo_dark');
+        if ($ids) {
+            $url = wp_get_attachment_image_url($ids[0], 'full');
             if ($url) return $url;
         }
         return self::logo_dark_url();