feat: Phase 0 — monorepo 骨架 + 全表迁移 + FastAPI/Next 骨架 + CI

- uv(workspace) + pnpm monorepo；docker-compose(pg+api+web)
- SQLAlchemy 16 MVP 表 + Alembic 初版迁移(无漂移，users stub)
- FastAPI 骨架：统一错误信封(带 request_id) + structlog + /jobs/:id + OpenAPI
- Next.js 骨架：纸感主题 token + OpenAPI→TS 客户端代码生成(gen:api)
- CI(ruff/mypy/pytest + pg service + alembic 漂移校验)
- 四份设计规格(PRODUCT/UX/ARCHITECTURE/DEV_PLAN) + CLAUDE.md

apps/web/components/LeftNav.tsx

@@ -0,0 +1,66 @@
+"use client";
+
+import Link from "next/link";
+import { usePathname } from "next/navigation";
+
+interface NavItem {
+  href: string;
+  label: string;
+  // M1 仅作品库 + 设置可达；其余为后续里程碑占位（禁用）。
+  enabled: boolean;
+}
+
+const NAV_ITEMS: NavItem[] = [
+  { href: "/", label: "作品库", enabled: true },
+  { href: "/settings/providers", label: "设置", enabled: true },
+  { href: "#outline", label: "大纲", enabled: false },
+  { href: "#codex", label: "设定库", enabled: false },
+  { href: "#foreshadow", label: "伏笔", enabled: false },
+  { href: "#review", label: "审稿", enabled: false },
+  { href: "#style", label: "文风", enabled: false },
+];
+
+// 左导航：当前项朱砂竖条 + 浅晕底（UX §5.1）。
+export function LeftNav() {
+  const pathname = usePathname();
+  return (
+    <nav
+      className="w-44 shrink-0 border-r border-line bg-panel py-4"
+      aria-label="主导航"
+    >
+      <ul className="flex flex-col gap-1 px-2">
+        {NAV_ITEMS.map((item) => {
+          const active = item.enabled && pathname === item.href;
+          if (!item.enabled) {
+            return (
+              <li key={item.label}>
+                <span
+                  className="block cursor-not-allowed rounded px-3 py-2 text-sm text-ink-soft/50"
+                  aria-disabled="true"
+                  title="后续里程碑开放"
+                >
+                  {item.label}
+                </span>
+              </li>
+            );
+          }
+          return (
+            <li key={item.label}>
+              <Link
+                href={item.href}
+                aria-current={active ? "page" : undefined}
+                className={`flex items-center gap-2 rounded px-3 py-2 text-sm ${
+                  active
+                    ? "border-l-2 border-cinnabar bg-[var(--color-cinnabar-wash)] text-cinnabar"
+                    : "text-ink hover:bg-[var(--color-cinnabar-wash)]"
+                }`}
+              >
+                {item.label}
+              </Link>
+            </li>
+          );
+        })}
+      </ul>
+    </nav>
+  );
+}