fix(chat): honor new-chat intent from secondary pages

Create a fresh local consultation for explicit new-chat navigation and keep reserved recovery from taking over its landing. Add regression tests and record validation gaps for remote review.

Co-Authored-By: Claude Code <noreply@anthropic.com>

frontend/src/components/app-sidebar.tsx

@@ -19,7 +19,7 @@ import { usePathname } from "next/navigation";
 import { useEffect, useRef } from "react";
 import type { Ref } from "react";
 import { AppLink } from "@/components/app-link";
-import { persistLoginSessionReturn, sessionHref } from "@/lib/chat-session-url";
+import { newChatHref, persistLoginSessionReturn, sessionHref } from "@/lib/chat-session-url";
 import { prefetchSecondaryPage } from "@/lib/secondary-page-data";
 import {
   Sidebar,
@@ -248,7 +248,7 @@ export function AppSidebar({
                 {showExpandedContent ? <span>{creatingSession ? "正在创建" : "新建对话"}</span> : null}
               </SidebarMenuButton>
             ) : (
-              <SidebarMenuLink className="new-chat" tooltip="新对话" href="/" onClick={closeDrawer}>
+              <SidebarMenuLink className="new-chat" tooltip="新对话" href={newChatHref()} onClick={closeDrawer}>
                 <SquarePen size={18} strokeWidth={1.75} aria-hidden="true" />
                 {showExpandedContent ? <span>新建对话</span> : null}
               </SidebarMenuLink>