feat: 首页 Go SSR 与 React hydrate 同构，消壳层与帖行闪动

补齐侧栏/右栏图标与徽章、鉴权种子、StaticFeedList，并修正嵌套 a 与标题徽章对齐。

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

frontend/src/utils/homeHydrate.ts

@@ -0,0 +1,41 @@
+/** 首页 SSR hydrate 首帧同构标志（仅 / 与板块首页） */
+
+declare global {
+  interface Window {
+    __J13_HYDRATING_HOME__?: boolean;
+  }
+}
+
+let hydrating = false;
+
+export function beginHomeHydrate() {
+  hydrating = true;
+  try {
+    window.__J13_HYDRATING_HOME__ = true;
+  } catch {
+    /* ignore */
+  }
+}
+
+export function endHomeHydrate() {
+  hydrating = false;
+  try {
+    delete window.__J13_HYDRATING_HOME__;
+  } catch {
+    try {
+      window.__J13_HYDRATING_HOME__ = undefined;
+    } catch {
+      /* ignore */
+    }
+  }
+}
+
+/** 首帧是否必须与 Go SSR DOM 同构 */
+export function isHomeHydrating(): boolean {
+  if (hydrating) return true;
+  try {
+    return !!window.__J13_HYDRATING_HOME__;
+  } catch {
+    return false;
+  }
+}