feat: Admin 媒体库列表、删除与同步索引

SSR /admin/media 复用 ListMedia/DeleteMedia，并支持按 ID 批量删与扫盘回填。

Co-authored-by: Cursor <cursoragent@cursor.com>

web_src/css/site.css

@@ -1046,6 +1046,72 @@ points-only[data-locked="false"] {
   gap: 0.5rem;
   align-items: center;
 }
+.j13-admin-media-toolbar {
+  display: flex;
+  flex-wrap: wrap;
+  gap: 0.75rem 1.25rem;
+  align-items: flex-end;
+  margin-bottom: 0.75rem;
+}
+.j13-admin-media-batch {
+  display: flex;
+  flex-wrap: wrap;
+  gap: 0.75rem;
+  align-items: center;
+  margin: 0 0 0.75rem;
+}
+.j13-admin-media-grid {
+  list-style: none;
+  margin: 0;
+  padding: 0;
+  display: grid;
+  grid-template-columns: repeat(auto-fill, minmax(11rem, 1fr));
+  gap: 0.85rem;
+}
+.j13-admin-media-card {
+  position: relative;
+  border: 1px solid var(--j13-border);
+  border-radius: 6px;
+  overflow: hidden;
+  background: var(--j13-surface, #fff);
+}
+.j13-admin-media-check {
+  position: absolute;
+  top: 0.4rem;
+  left: 0.4rem;
+  z-index: 1;
+  background: rgba(255,255,255,0.85);
+  border-radius: 3px;
+  padding: 0.1rem 0.2rem;
+}
+.j13-admin-media-thumb {
+  display: block;
+  aspect-ratio: 1;
+  background: var(--j13-bg, #f5f5f5);
+}
+.j13-admin-media-thumb img {
+  width: 100%;
+  height: 100%;
+  object-fit: cover;
+  display: block;
+}
+.j13-admin-media-meta {
+  padding: 0.45rem 0.55rem 0.6rem;
+  font-size: 0.85rem;
+}
+.j13-admin-media-name {
+  overflow: hidden;
+  text-overflow: ellipsis;
+  white-space: nowrap;
+  font-weight: 600;
+}
+.j13-admin-media-ops {
+  display: flex;
+  flex-wrap: wrap;
+  gap: 0.5rem;
+  align-items: center;
+  margin-top: 0.35rem;
+}
 .j13-post__admin {
   display: flex;
   flex-wrap: wrap;