feat(ux): M1/M2 移动端可用 — 导航汉堡抽屉 + 写作工具条不溢出

M1 左导航响应式抽屉：抽出 lib/nav/items.ts（条目数据+激活判定，纯逻辑+vitest）
共用于桌面静态侧栏（hidden lg:block）与移动汉堡抽屉。新增通用 Drawer（遮罩/
Esc 关闭/打开聚焦，复用 CommandPalette a11y 模式）+ NavDrawer + NavItems；
LeftNav 改 <lg 隐藏，AppShell 顶栏加汉堡（aria-label 打开导航）。

M2 写作工具条不溢出 + 移动端可达章节/助手：Toolbar 改 flex-wrap，390px 不再
横切「尚未保存」；ChapterList/ChapterAssistant 抽出 *Content，Workbench 经
左/右 Drawer 在 <lg 触达目录/助手。

实景 390px 复验（browse）：汉堡显示/静态导航隐藏/抽屉开合聚焦+Esc、工具条
两行不溢出、助手抽屉真注入面板。门禁：lint/typecheck 干净 · vitest 177 · build OK。

apps/web/lib/nav/items.test.ts

@@ -0,0 +1,72 @@
+import { describe, expect, it } from "vitest";
+
+import {
+  GLOBAL_NAV_ITEMS,
+  isNavItemActive,
+  projectNavItems,
+  type NavItem,
+} from "./items";
+
+const PID = "p1";
+
+describe("projectNavItems", () => {
+  it("builds the eight project entries scoped to the project id", () => {
+    const items = projectNavItems(PID);
+
+    expect(items).toHaveLength(8);
+    expect(items.map((i) => i.key)).toEqual([
+      "write",
+      "outline",
+      "foreshadow",
+      "review",
+      "style",
+      "codex",
+      "rules",
+      "skills",
+    ]);
+    expect(items.every((i) => i.href.startsWith(`/projects/${PID}/`))).toBe(
+      true,
+    );
+  });
+});
+
+describe("isNavItemActive", () => {
+  const write: NavItem = {
+    href: `/projects/${PID}/write`,
+    label: "写作",
+    key: "write",
+  };
+
+  it("matches a project item by its activeNav key regardless of pathname", () => {
+    expect(
+      isNavItemActive(write, { pathname: "/anything", activeNav: "write" }),
+    ).toBe(true);
+  });
+
+  it("matches a project item by exact pathname when no activeNav given", () => {
+    expect(isNavItemActive(write, { pathname: `/projects/${PID}/write` })).toBe(
+      true,
+    );
+  });
+
+  it("does not match a project item when neither key nor path align", () => {
+    expect(isNavItemActive(write, { pathname: "/", activeNav: "outline" })).toBe(
+      false,
+    );
+  });
+
+  it("matches a global item by exact pathname only", () => {
+    const works = GLOBAL_NAV_ITEMS[0];
+    expect(isNavItemActive(works, { pathname: "/" })).toBe(true);
+    expect(isNavItemActive(works, { pathname: "/projects/p1/write" })).toBe(
+      false,
+    );
+  });
+
+  it("ignores activeNav for global items (no key)", () => {
+    const settings = GLOBAL_NAV_ITEMS[1];
+    expect(
+      isNavItemActive(settings, { pathname: "/", activeNav: "write" }),
+    ).toBe(false);
+  });
+});