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

backend/app/models/field_mapping.py

@@ -0,0 +1,43 @@
+"""
+字段映射模型
+
+用于存储 AI 识别的字段映射结果
+"""
+
+from datetime import datetime
+from typing import List, Optional
+
+from sqlalchemy import ForeignKey, Integer, String, Float, Boolean, DateTime, JSON, Text
+from sqlalchemy.orm import Mapped, mapped_column, relationship
+
+from app.models.base import BaseModel
+
+
+class FieldMapping(BaseModel):
+    """
+    字段映射模型
+
+    记录源字段到标准字段的映射关系
+    """
+
+    __tablename__ = "field_mappings"
+
+    company_id: Mapped[int] = mapped_column(Integer, ForeignKey("companies.id"), nullable=False, index=True)
+    file_id: Mapped[int] = mapped_column(Integer, ForeignKey("uploaded_files.id"), nullable=False, index=True)
+    source_field: Mapped[str] = mapped_column(String(100), nullable=False, comment="源字段名")
+    standard_field: Mapped[str] = mapped_column(String(100), nullable=False, comment="标准字段名")
+    confidence: Mapped[float] = mapped_column(Float, nullable=False, default=0.0, comment="置信度 0-1")
+    confirmed: Mapped[bool] = mapped_column(Boolean, nullable=False, default=False, comment="是否已确认")
+    confirmed_by: Mapped[Optional[int]] = mapped_column(Integer, ForeignKey("users.id"), nullable=True)
+    confirmed_at: Mapped[Optional[datetime]] = mapped_column(DateTime, nullable=True)
+    sample_values: Mapped[Optional[dict]] = mapped_column(JSON, nullable=True, comment="样例值")
+    reasoning: Mapped[Optional[str]] = mapped_column(Text, nullable=True, comment="AI 判断依据")
+    is_skipped: Mapped[bool] = mapped_column(Boolean, nullable=False, default=False, comment="是否跳过")
+
+    # 关系
+    company = relationship("Company", back_populates="field_mappings")
+    file = relationship("UploadedFile", back_populates="field_mappings")
+    confirmed_by_user = relationship("User", foreign_keys=[confirmed_by])
+
+    def __repr__(self) -> str:
+        return f"<FieldMapping(source='{self.source_field}' -> standard='{self.standard_field}', confidence={self.confidence})>"