fix(yiyan): stop invalid Hitokoto category requests

Public hitokoto v1 rejects c=hitokoto (and ignores batch count). Whitelist
categories a–l, multi-fetch for carousel, and share full markup via
aksrt_render_yiyan_block so single-post shells actually render quotes.

inc/helpers/aksrt-yiyan.php

@@ -0,0 +1,55 @@
+<?php
+/**
+ * 一言 (Hitokoto) markup helper.
+ *
+ * Shared shell for single-post placements and the yiyan widget.
+ *
+ * @package AKSRT
+ */
+
+defined('ABSPATH') || exit;
+
+if (!function_exists('aksrt_render_yiyan_block')) :
+	/**
+	 * Shared 一言 shell for single-post placements (and reusable markup).
+	 *
+	 * Hitokoto category `c` must be a letter a–l, or empty for mixed random.
+	 * Client loads quotes via parallel fetches when count > 1.
+	 *
+	 * @param array<string,mixed> $args {
+	 *     @type string $class    Extra CSS classes on the root.
+	 *     @type string $type     Category letter a–l, or empty for random.
+	 *     @type int    $count    Number of quotes to load (1–10).
+	 *     @type int    $interval Rotation interval in seconds.
+	 *     @type string $icon     Optional FA icon class; empty = no icon.
+	 * }
+	 */
+	function aksrt_render_yiyan_block(array $args = []): void {
+		$class    = trim((string) ($args['class'] ?? 'aksrt-yiyan'));
+		$type_raw = strtolower(trim((string) ($args['type'] ?? '')));
+		$type     = preg_match('/^[a-l]$/', $type_raw) ? $type_raw : '';
+		$count    = max(1, min(10, (int) ($args['count'] ?? 5)));
+		$interval = max(3, min(30, (int) ($args['interval'] ?? 8)));
+		$icon     = sanitize_text_field((string) ($args['icon'] ?? ''));
+
+		if (strpos($class, 'aksrt-yiyan') === false) {
+			$class = trim($class . ' aksrt-yiyan');
+		}
+		?>
+		<div class="<?php echo esc_attr($class); ?>"
+			data-aksrt-yiyan
+			data-count="<?php echo esc_attr((string) $count); ?>"
+			data-interval="<?php echo esc_attr((string) $interval); ?>"
+			<?php echo $type !== '' ? ' data-type="' . esc_attr($type) . '"' : ''; ?>>
+			<div class="aksrt-yiyan__content">
+				<?php if ($icon !== '') : ?>
+					<i class="<?php echo esc_attr($icon); ?> aksrt-yiyan__icon" aria-hidden="true"></i>
+				<?php endif; ?>
+				<p class="aksrt-yiyan__text"><?php esc_html_e('加载中…', 'aksrt'); ?></p>
+				<p class="aksrt-yiyan__from"></p>
+			</div>
+			<div class="aksrt-yiyan__dots" aria-hidden="true"></div>
+		</div>
+		<?php
+	}
+endif;