feat(web): home media sections use 5-up PC / 1-up mobile grid, growth top5

reaction_board/web/static/style.css

@@ -415,17 +415,11 @@ a.live-chip:hover { border-color: color-mix(in srgb, var(--accent) 55%, var(--bo
   font-size: 18px;
 }
 
-.heat-strip {
-  display: grid;
-  grid-auto-flow: column;
-  grid-auto-columns: 210px;
-  gap: 10px;
-  overflow-x: auto;
-  padding-bottom: 4px;
-  scroll-snap-type: x proximity;
-  scrollbar-width: none;
-}
-.heat-strip::-webkit-scrollbar { display: none; }
+/* 统一的响应式媒体网格：移动端 1 列，PC 端 5 列。 */
+.media-grid { display: grid; grid-template-columns: minmax(0, 1fr); gap: 10px; }
+@media (min-width: 620px) { .media-grid { grid-template-columns: repeat(2, minmax(0, 1fr)); } }
+@media (min-width: 900px) { .media-grid { grid-template-columns: repeat(3, minmax(0, 1fr)); } }
+@media (min-width: 1280px) { .media-grid { grid-template-columns: repeat(5, minmax(0, 1fr)); } }
 /* 统一的竖排媒体卡：图 + 两行截断标题 + 作者/数据行 + 高亮数据行。 */
 .media-card {
   position: relative;
@@ -442,7 +436,6 @@ a.live-chip:hover { border-color: color-mix(in srgb, var(--accent) 55%, var(--bo
   border-color: color-mix(in srgb, var(--accent) 55%, var(--border));
   transform: translateY(-1px);
 }
-.heat-strip > .media-card { scroll-snap-align: start; }
 .media-rank {
   position: absolute;
   top: 10px;