feat: 完善前后端核心功能模块

后端:
- 新增认证(auth)、任务(tasks)、映射(mappings)、对账(reconciliation)、异常(exceptions)、导出(exports) API
- 新增核心模块: database, security, permissions, tenant, exceptions, error_handlers
- 新增数据模型: user, company, reconciliation_task, field_mapping, uploaded_file 等
- 新增服务层: ai_recognizer, file_parser, file_storage, mapping, reconciliation 等
- 添加数据库迁移脚本

前端:
- 新增登录页面和仪表盘页面
- 新增任务列表、任务详情、字段映射页面
- 新增异常处理页面和规则设置页面
- 新增 API 代理路由 /api/[...path]
- 新增 UI 组件库 (button, card, dialog, input, table 等)
- 新增 auth 组件 (ProtectedRoute, PermissionGate)
- 新增 layout 组件 (Header, Sidebar)
- 新增 mapping 组件 (FieldMappingTable, AISuggestionPanel)
- 新增 API 客户端和 hooks (useAsync, useToast, usePermission 等)
- 新增状态管理 (auth-store, company-store, ui-store)
- 集成 Tailwind CSS 和 shadcn/ui 组件库

其他:
- 添加 Alembic 数据库迁移配置
- 添加初始化示例数据脚本
- 更新项目文档

frontend/components/layout/Sidebar.tsx

@@ -0,0 +1,105 @@
+"use client";
+
+import Link from "next/link";
+import { usePathname } from "next/navigation";
+import { motion } from "motion/react";
+import { 
+  LayoutDashboard, 
+  FileText, 
+  AlertTriangle, 
+  Settings,
+  ChevronLeft,
+  ChevronRight
+} from "lucide-react";
+import { cn } from "@/lib/utils";
+import { useState } from "react";
+
+const navItems = [
+  { 
+    label: "工作台", 
+    href: "/dashboard", 
+    icon: LayoutDashboard 
+  },
+  { 
+    label: "对账任务", 
+    href: "/tasks", 
+    icon: FileText 
+  },
+  { 
+    label: "异常处理", 
+    href: "/exceptions", 
+    icon: AlertTriangle 
+  },
+  { 
+    label: "规则设置", 
+    href: "/settings/rules", 
+    icon: Settings 
+  },
+];
+
+export function Sidebar() {
+  const pathname = usePathname();
+  const [collapsed, setCollapsed] = useState(false);
+
+  return (
+    <aside 
+      className={cn(
+        "sticky top-14 h-[calc(100vh-3.5rem)] border-r border-border bg-background transition-all duration-300 flex flex-col",
+        collapsed ? "w-16" : "w-56"
+      )}
+    >
+      {/* Navigation */}
+      <nav className="flex-1 p-3 space-y-1">
+        {navItems.map((item) => {
+          const isActive = pathname === item.href || pathname.startsWith(item.href + "/");
+          const Icon = item.icon;
+          
+          return (
+            <Link
+              key={item.href}
+              href={item.href}
+              className={cn(
+                "flex items-center gap-3 px-3 py-2.5 rounded-lg transition-all relative group",
+                isActive 
+                  ? "bg-primary/10 text-primary" 
+                  : "text-muted-foreground hover:bg-muted hover:text-foreground",
+                collapsed && "justify-center px-0"
+              )}
+            >
+              {isActive && (
+                <motion.div
+                  layoutId="activeNav"
+                  className="absolute inset-0 bg-primary/10 rounded-lg -z-10"
+                  transition={{ type: "spring", bounce: 0.2, duration: 0.4 }}
+                />
+              )}
+              <Icon className={cn("w-5 h-5 shrink-0", isActive && "text-primary")} />
+              {!collapsed && (
+                <span className="text-body font-medium">{item.label}</span>
+              )}
+              
+              {/* Tooltip for collapsed state */}
+              {collapsed && (
+                <div className="absolute left-full ml-2 px-2 py-1 bg-foreground text-background text-xs rounded opacity-0 invisible group-hover:opacity-100 group-hover:visible transition-all whitespace-nowrap z-50">
+                  {item.label}
+                </div>
+              )}
+            </Link>
+          );
+        })}
+      </nav>
+
+      {/* Collapse toggle */}
+      <button
+        onClick={() => setCollapsed(!collapsed)}
+        className="flex items-center justify-center h-10 border-t border-border text-muted-foreground hover:text-foreground hover:bg-muted transition-colors"
+      >
+        {collapsed ? (
+          <ChevronRight className="w-4 h-4" />
+        ) : (
+          <ChevronLeft className="w-4 h-4" />
+        )}
+      </button>
+    </aside>
+  );
+}