fix(homepage): make post stream visible (panel opacity + posts display)

Active homepage tab pane was stuck at opacity:0, and custom <posts>
elements lacked display:block, so published items rendered in HTML but
were effectively invisible. Style list cards under #index-tab-main too.

assets/css/frontend/post-card.css

@@ -26,6 +26,8 @@
  * 通用 posts-item 基础 — 对齐 zibll line 7585
  * ============================================================ */
 .posts-item {
+    /* Custom element <posts> is inline by default — force block layout. */
+    display: block;
     padding: 20px;
     margin: 15px 0;
     background: var(--main-bg-color, var(--surface-1, #fff));
@@ -34,6 +36,22 @@
     transition: box-shadow 0.2s ease;
     box-shadow: 0 0 10px var(--main-shadow, var(--shadow-sm));
     border-radius: var(--main-radius, var(--radius, 8px));
+    font-size: 1rem;
+    color: var(--main-color, #4e5358);
+    opacity: 1;
+}
+
+.posts-item.list {
+    display: block;
+    width: 100%;
+    font-size: 1rem;
+}
+
+/* No-thumb list cards: body fills full width (no float hole for missing thumb). */
+.posts-item.list.no-thumb .item-body,
+.posts-item.no-thumb .item-body {
+    width: 100%;
+    margin: 0;
 }
 
 /* ============================================================