style(secondary-nav): 二级导航统一改为水平居中，主导航保持靠右不变;

- 将 5 个模块二级导航（KnowledgeNav / InterfaceNav / MemoryNav / HomeNav / AdminNav）的外层 flex 容器由 justify-end 调整为 justify-center，使胶囊样导航整体水平居中；
- 同步更新 KnowledgeNav 视觉不变量单测，断言 className 包含 justify-center 且同时排除 justify-end / justify-between，防止误回退；
- 主导航 MainNav（SiteHeader 内）继续通过 justify-between 实现靠右，不动。

🤖 Generated with [Claude Code](https://github.com/claude), [CodeX](https://openai.com), [Gemini](https://github.com/apps/gemini-code-assist)
Co-Authored-By: Aurelius Huang<threefish.ai@gmail.com>

Author: ThreeFish-AI

apps/negentropy-ui/components/ui/AdminNav.tsx

@@ -31,7 +31,7 @@ export function AdminNav({
 
   return (
     <div className="border-b border-border bg-card px-6 py-1">
-      <div className="flex flex-wrap items-center justify-end gap-4">
+      <div className="flex flex-wrap items-center justify-center gap-4">
         <nav className="flex flex-wrap items-center gap-1 bg-muted/50 p-1 rounded-full">
           {NAV_ITEMS.map((item) => (
             <Link

apps/negentropy-ui/components/ui/HomeNav.tsx

@@ -38,7 +38,7 @@ export function HomeNav({ title }: { title: string }) {
 
   return (
     <div className="border-b border-border bg-card px-6 py-1">
-      <div className="flex flex-wrap items-center justify-end gap-4">
+      <div className="flex flex-wrap items-center justify-center gap-4">
         <nav className="flex items-center gap-1 bg-muted/50 p-1 rounded-full">
           {NAV_ITEMS.map((item) => {
             const href = item.key === "studio" ? studioHref : item.href;

apps/negentropy-ui/components/ui/InterfaceNav.tsx

@@ -44,7 +44,7 @@ export function InterfaceNav({
 
   return (
     <div className="border-b border-border bg-card px-6 py-1">
-      <div className="flex flex-wrap items-center justify-end gap-4">
+      <div className="flex flex-wrap items-center justify-center gap-4">
         <nav className="flex flex-wrap items-center gap-1 bg-muted/50 p-1 rounded-full">
           {visibleItems.map((item) => (
             <Link

apps/negentropy-ui/components/ui/KnowledgeNav.tsx

@@ -37,7 +37,7 @@ export function KnowledgeNav({
 
   return (
     <div className="border-b border-border bg-card px-6 py-1">
-      <div className="flex flex-wrap items-center justify-end gap-4">
+      <div className="flex flex-wrap items-center justify-center gap-4">
         {modeToggle}
         <nav className="flex items-center gap-1 bg-muted/50 p-1 rounded-full">
           {NAV_ITEMS.map((item) => {

apps/negentropy-ui/components/ui/MemoryNav.tsx

@@ -36,7 +36,7 @@ export function MemoryNav({
 
   return (
     <div className="border-b border-border bg-card px-6 py-1">
-      <div className="flex flex-wrap items-center justify-end gap-4">
+      <div className="flex flex-wrap items-center justify-center gap-4">
         <nav className="flex items-center gap-1 bg-muted/50 p-1 rounded-full">
           {NAV_ITEMS.map((item) => (
             <Link

apps/negentropy-ui/tests/unit/ui/KnowledgeNav.test.tsx

@@ -26,17 +26,18 @@ describe("KnowledgeNav", () => {
     expect(baseLink).toHaveAttribute("href", "/knowledge/base");
   });
 
-  // 视觉不变量：与 HomeNav/MemoryNav/InterfaceNav/AdminNav 保持二级导航靠右对齐
-  it("二级导航容器使用 justify-end，整体右对齐", () => {
+  // 视觉不变量：与 HomeNav/MemoryNav/InterfaceNav/AdminNav 保持二级导航水平居中
+  it("二级导航容器使用 justify-center，整体水平居中", () => {
     const { container } = render(<KnowledgeNav title="Pipelines" />);
     const nav = container.querySelector("nav") as HTMLElement;
     const flexRow = nav.parentElement as HTMLElement;
 
-    expect(flexRow.className).toContain("justify-end");
+    expect(flexRow.className).toContain("justify-center");
+    expect(flexRow.className).not.toContain("justify-end");
     expect(flexRow.className).not.toContain("justify-between");
   });
 
-  it("传入 modeToggle 时，渲染顺序为 modeToggle 在 nav 之前（确保 nav 始终贴最右边缘）", () => {
+  it("传入 modeToggle 时，渲染顺序为 modeToggle 在 nav 之前（确保 modeToggle 与 nav 顺序稳定）", () => {
     const { container } = render(
       <KnowledgeNav title="Wiki" modeToggle={<div data-testid="mt">toggle</div>} />,
     );