refactor(frontend): 删顶部「AI 工具条」，--chrome 归位 4rem（写作台 UX P0-3）

顶栏「AI 工具条」5 项全是重复左栏的导航链接，且让「写本章」同时是导航
Link 与生成动作两种相反含义。删掉后导航只归左栏，同时消灭最严重的三重复
+ 假「AI」标签 + 「写本章」双重含义，并省下 48px（--chrome 7rem→4rem）。
死代码 AiToolbar/AiToolbarMoreMenu/ai-tools 全仓仅 AppShell 引用，一并移除。

apps/web/components/AiToolbar.tsx

@@ -1,93 +0,0 @@
-import Link from "next/link";
-import {
-  BookOpen,
-  ClipboardCheck,
-  ListTree,
-  PenLine,
-  Sparkles,
-  type LucideIcon,
-} from "lucide-react";
-
-import { AiToolbarMoreMenu } from "@/components/AiToolbarMoreMenu";
-import {
-  aiToolItems,
-  primaryAiToolItems,
-  secondaryAiToolItems,
-} from "@/lib/nav/ai-tools";
-import type { ActiveNav } from "@/lib/nav/items";
-import { buttonClass } from "@/lib/ui/variants";
-
-interface AiToolbarProps {
-  projectId: string;
-  activeNav?: ActiveNav;
-}
-
-// T4-a · 项目内页常驻 AI 工具条（顶栏下，UX §3/§5）。
-// 桌面展示完整工具条；窄屏只保留写本章/审稿，把低频入口收进更多菜单。
-export function AiToolbar({ projectId, activeNav }: AiToolbarProps) {
-  const primaryItems = primaryAiToolItems(projectId);
-  const secondaryItems = secondaryAiToolItems(projectId);
-  return (
-    <nav
-      aria-label="AI 工具条"
-      className="sticky top-16 z-20 flex h-12 items-center gap-2 border-b border-line bg-panel px-4 sm:px-6"
-    >
-      <div className="flex min-w-0 flex-1 items-center gap-2 overflow-hidden lg:hidden">
-        {primaryItems.map((item) => {
-          const isActive = item.key === activeNav;
-          const className = toolClassName(item.primary === true, isActive);
-          const Icon = toolIcon(item.key);
-          return (
-            <Link
-              key={item.href}
-              href={item.href}
-              aria-current={isActive ? "page" : undefined}
-              className={className}
-            >
-              <Icon className="h-4 w-4" aria-hidden="true" />
-              <span>{item.label}</span>
-            </Link>
-          );
-        })}
-        <AiToolbarMoreMenu items={secondaryItems} activeNav={activeNav} />
-      </div>
-
-      <div className="hidden items-center gap-2 overflow-x-auto whitespace-nowrap lg:flex">
-        {aiToolItems(projectId).map((item) => {
-          const isActive = item.key === activeNav;
-          const className = toolClassName(item.primary === true, isActive);
-          const Icon = toolIcon(item.key);
-          return (
-            <Link
-              key={item.href}
-              href={item.href}
-              aria-current={isActive ? "page" : undefined}
-              className={className}
-            >
-              <Icon className="h-4 w-4" aria-hidden="true" />
-              <span>{item.label}</span>
-            </Link>
-          );
-        })}
-      </div>
-    </nav>
-  );
-}
-
-function toolIcon(key: ActiveNav): LucideIcon {
-  if (key === "write") return PenLine;
-  if (key === "review") return ClipboardCheck;
-  if (key === "outline") return ListTree;
-  if (key === "codex") return BookOpen;
-  return Sparkles;
-}
-
-function toolClassName(isPrimary: boolean, isActive: boolean): string {
-  if (isActive) {
-    return buttonClass({ variant: "outline", size: "sm" });
-  }
-  if (isPrimary) {
-    return buttonClass({ variant: "primary", size: "sm" });
-  }
-  return buttonClass({ variant: "secondary", size: "sm" });
-}

apps/web/components/AiToolbarMoreMenu.tsx

@@ -1,95 +0,0 @@
-"use client";
-
-import Link from "next/link";
-import { MoreHorizontal } from "lucide-react";
-import { useEffect, useId, useRef, useState } from "react";
-
-import type { AiToolItem } from "@/lib/nav/ai-tools";
-import type { ActiveNav } from "@/lib/nav/items";
-import { buttonClass, cn, focusRing } from "@/lib/ui/variants";
-
-interface AiToolbarMoreMenuProps {
-  items: AiToolItem[];
-  activeNav?: ActiveNav;
-}
-
-export function AiToolbarMoreMenu({
-  items,
-  activeNav,
-}: AiToolbarMoreMenuProps) {
-  const [open, setOpen] = useState(false);
-  const menuId = useId();
-  const rootRef = useRef<HTMLDivElement>(null);
-  const buttonRef = useRef<HTMLButtonElement>(null);
-
-  useEffect(() => {
-    if (!open) return;
-
-    const onKeyDown = (event: KeyboardEvent): void => {
-      if (event.key === "Escape") {
-        setOpen(false);
-        buttonRef.current?.focus();
-      }
-    };
-
-    const onPointerDown = (event: PointerEvent): void => {
-      const target = event.target;
-      if (target instanceof Node && !rootRef.current?.contains(target)) {
-        setOpen(false);
-      }
-    };
-
-    window.addEventListener("keydown", onKeyDown);
-    window.addEventListener("pointerdown", onPointerDown);
-    return () => {
-      window.removeEventListener("keydown", onKeyDown);
-      window.removeEventListener("pointerdown", onPointerDown);
-    };
-  }, [open]);
-
-  return (
-    <div ref={rootRef} className="relative">
-      <button
-        ref={buttonRef}
-        type="button"
-        aria-haspopup="true"
-        aria-expanded={open}
-        aria-controls={menuId}
-        onClick={() => setOpen((value) => !value)}
-        className={buttonClass({ variant: "secondary", size: "sm" })}
-      >
-        <MoreHorizontal className="h-4 w-4" aria-hidden="true" />
-        更多
-      </button>
-      {open ? (
-        // 诚实的 Tab-only 折叠面板：普通导航链接，不冒充 ARIA menu（无 roving tabindex/方向键）。
-        <nav
-          id={menuId}
-          aria-label="更多工具"
-          className="absolute right-0 z-30 mt-2 min-w-36 rounded border border-line bg-panel p-1 shadow-paper"
-        >
-          {items.map((item) => {
-            const active = item.key === activeNav;
-            return (
-              <Link
-                key={item.href}
-                href={item.href}
-                aria-current={active ? "page" : undefined}
-                onClick={() => setOpen(false)}
-                className={cn(
-                  "block rounded px-3 py-2 text-sm transition-colors",
-                  focusRing,
-                  active
-                    ? "bg-[var(--color-cinnabar-wash)] text-cinnabar"
-                    : "text-ink hover:bg-bg hover:text-cinnabar",
-                )}
-              >
-                {item.label}
-              </Link>
-            );
-          })}
-        </nav>
-      ) : null}
-    </div>
-  );
-}

apps/web/components/AppShell.tsx

@@ -4,7 +4,6 @@ import { Settings } from "lucide-react";
 
 import type { ActiveNav } from "@/lib/nav/items";
 import { buttonClass, focusRing } from "@/lib/ui/variants";
-import { AiToolbar } from "./AiToolbar";
 import { CommandSearchButton } from "./command/CommandPaletteMount";
 import { LeftNav } from "./LeftNav";
 import { NavDrawer } from "./NavDrawer";
@@ -32,7 +31,7 @@ export function AppShell({
   return (
     <div
       className="min-h-screen"
-      style={{ ["--chrome" as string]: projectId ? "7rem" : "4rem" }}
+      style={{ ["--chrome" as string]: "4rem" }}
     >
       <a
         href="#main"
@@ -80,9 +79,6 @@ export function AppShell({
           </Link>
         </nav>
       </header>
-      {projectId ? (
-        <AiToolbar projectId={projectId} activeNav={activeNav} />
-      ) : null}
       <div className="flex">
         <LeftNav projectId={projectId} activeNav={activeNav} />
         <main