refactor(router): introduce app navigation manager

src/app/chat/components/chat-header.tsx

@@ -7,9 +7,9 @@
  */
 import type { ReactNode } from "react";
 import { Lock, Menu } from "lucide-react";
-import { useRouter } from "next/navigation";
 
 import { ROUTES } from "@/router/routes";
+import { useAppNavigator } from "@/router/use-app-navigator";
 
 import styles from "./chat-header.module.css";
 
@@ -19,7 +19,7 @@ export interface ChatHeaderProps {
 }
 
 export function ChatHeader({ isGuest, offerBanner }: ChatHeaderProps) {
-  const router = useRouter();
+  const navigator = useAppNavigator();
 
   if (isGuest) {
     return (
@@ -27,7 +27,7 @@ export function ChatHeader({ isGuest, offerBanner }: ChatHeaderProps) {
         <button
           type="button"
           className={styles.guestBanner}
-          onClick={() => router.push(ROUTES.auth)}
+          onClick={() => navigator.openAuth(ROUTES.chat)}
           aria-label="Sign up to unlock more features"
         >
           <Lock className={styles.guestBannerIcon} size={16} aria-hidden="true" />
@@ -46,7 +46,7 @@ export function ChatHeader({ isGuest, offerBanner }: ChatHeaderProps) {
         <button
           type="button"
           className={styles.menuButton}
-          onClick={() => router.push(ROUTES.sidebar)}
+          onClick={() => navigator.push(ROUTES.sidebar)}
           aria-label="Menu"
         >
           <Menu className={styles.menuIcon} size={24} aria-hidden="true" />

src/app/chat/components/chat-insufficient-credits-banner.tsx

@@ -16,9 +16,7 @@
  * 不做的事：
  *   - 不直接管理 state machine（chat 机器不感知 UI 层）
  */
-import { useRouter } from "next/navigation";
-
-import { ROUTE_BUILDERS } from "@/router/routes";
+import { useAppNavigator } from "@/router/use-app-navigator";
 
 import styles from "./chat-insufficient-credits-banner.module.css";
 
@@ -26,7 +24,7 @@ export interface ChatInsufficientCreditsBannerProps {
   title?: string;
   ctaLabel?: string;
   /**
-   * 自定义点击回调（不传则默认 router.push(topup subscription)）
+   * 自定义点击回调（不传则默认走统一订阅导航）
    * - 测试时可传 mock
    * - 嵌入其他场景时（如 nested overlay）可传自定义
    */
@@ -38,7 +36,7 @@ export function ChatInsufficientCreditsBanner({
   ctaLabel = "Top up credits to continue",
   onUnlock,
 }: ChatInsufficientCreditsBannerProps) {
-  const router = useRouter();
+  const navigator = useAppNavigator();
   const titleLines = title.split("\n");
 
   const handleClick = () => {
@@ -46,7 +44,7 @@ export function ChatInsufficientCreditsBanner({
       onUnlock();
       return;
     }
-    router.push(ROUTE_BUILDERS.subscription("topup"));
+    navigator.openSubscription({ type: "topup", returnTo: "chat" });
   };
 
   return (