feat(widgets): AKSRT image slider widget

Lightweight multi-slide carousel with captions, dots, arrows, and CSS
bundled via widgets.css import; registered in widgets-register.

assets/css/frontend/widget-slider.css

@@ -0,0 +1,93 @@
+/**
+ * Widget slider (AKSRT 幻灯片).
+ * @package AKSRT
+ */
+.aksrt-widget-slider {
+  position: relative;
+  overflow: hidden;
+  border-radius: 8px;
+  background: var(--surface-2, #f3f4f6);
+}
+.aksrt-widget-slider__track {
+  position: relative;
+  width: 100%;
+  height: var(--aksrt-slider-h, 220px);
+}
+.aksrt-widget-slider__slide {
+  position: absolute;
+  inset: 0;
+  opacity: 0;
+  pointer-events: none;
+  transition: opacity .35s ease;
+}
+.aksrt-widget-slider__slide.is-active {
+  opacity: 1;
+  pointer-events: auto;
+  z-index: 1;
+}
+.aksrt-widget-slider__slide img,
+.aksrt-widget-slider__link {
+  display: block;
+  width: 100%;
+  height: 100%;
+  object-fit: cover;
+}
+.aksrt-widget-slider__caption {
+  position: absolute;
+  left: 0;
+  right: 0;
+  bottom: 0;
+  padding: 10px 12px;
+  background: linear-gradient(transparent, rgba(0,0,0,.55));
+  color: #fff;
+  display: flex;
+  flex-direction: column;
+  gap: 2px;
+  font-size: 13px;
+}
+.aksrt-widget-slider__caption strong {
+  font-size: 14px;
+}
+.aksrt-widget-slider__prev,
+.aksrt-widget-slider__next {
+  position: absolute;
+  top: 50%;
+  transform: translateY(-50%);
+  z-index: 2;
+  width: 28px;
+  height: 28px;
+  border: 0;
+  border-radius: 50%;
+  background: rgba(0,0,0,.35);
+  color: #fff;
+  cursor: pointer;
+  line-height: 28px;
+  text-align: center;
+  padding: 0;
+}
+.aksrt-widget-slider__prev { left: 8px; }
+.aksrt-widget-slider__next { right: 8px; }
+.aksrt-widget-slider__dots {
+  position: absolute;
+  left: 0;
+  right: 0;
+  bottom: 8px;
+  z-index: 2;
+  display: flex;
+  justify-content: center;
+  gap: 6px;
+  pointer-events: none;
+}
+.aksrt-widget-slider__dot {
+  pointer-events: auto;
+  width: 7px;
+  height: 7px;
+  border-radius: 50%;
+  border: 0;
+  padding: 0;
+  background: rgba(255,255,255,.45);
+  cursor: pointer;
+}
+.aksrt-widget-slider__dot.is-active {
+  background: #fff;
+}

assets/css/frontend/widgets.css

@@ -2,3 +2,4 @@
 @import url("widgets/part-2.css");
 @import url("widgets/part-3.css");
 @import url("widgets/part-4.css");
+@import url("widget-slider.css");