feat: 添加后端核心模块

用户认证：
- User 模型（支持邮箱/手机号登录）
- 双 Token JWT 认证（accessToken + refreshToken）
- 注册/登录/刷新 Token API

组织模型：
- Brand（品牌方）、Agency（代理商）、Creator（达人）
- 多对多关系：品牌方↔代理商、代理商↔达人

项目与任务：
- Project 模型（品牌方发布）
- Task 模型（完整审核流程追踪）
- Brief 模型（解析后的结构化内容）

文件上传：
- 阿里云 OSS 直传签名服务
- 支持分片上传，最大 500MB

数据库迁移：
- 003_user_org_project_task.py

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

backend/app/schemas/auth.py

@@ -0,0 +1,120 @@
+"""
+认证相关 Schema
+"""
+from typing import Optional
+from pydantic import BaseModel, EmailStr, Field
+from app.models.user import UserRole
+
+
+# ===== 请求 =====
+
+class RegisterRequest(BaseModel):
+    """注册请求"""
+    email: Optional[EmailStr] = None
+    phone: Optional[str] = Field(None, pattern=r"^1[3-9]\d{9}$")
+    password: str = Field(..., min_length=6, max_length=128)
+    name: str = Field(..., min_length=1, max_length=100)
+    role: UserRole
+
+    class Config:
+        json_schema_extra = {
+            "example": {
+                "email": "user@example.com",
+                "password": "password123",
+                "name": "张三",
+                "role": "creator"
+            }
+        }
+
+
+class LoginRequest(BaseModel):
+    """登录请求（邮箱或手机号）"""
+    email: Optional[EmailStr] = None
+    phone: Optional[str] = None
+    password: Optional[str] = None
+    sms_code: Optional[str] = None  # 短信验证码
+
+    class Config:
+        json_schema_extra = {
+            "example": {
+                "email": "user@example.com",
+                "password": "password123"
+            }
+        }
+
+
+class RefreshTokenRequest(BaseModel):
+    """刷新 Token 请求"""
+    refresh_token: str
+
+
+class SendSmsCodeRequest(BaseModel):
+    """发送短信验证码请求"""
+    phone: str = Field(..., pattern=r"^1[3-9]\d{9}$")
+
+
+class BindPhoneRequest(BaseModel):
+    """绑定手机号请求"""
+    phone: str = Field(..., pattern=r"^1[3-9]\d{9}$")
+    sms_code: str
+
+
+class BindEmailRequest(BaseModel):
+    """绑定邮箱请求"""
+    email: EmailStr
+    password: str = Field(..., min_length=6, max_length=128)
+
+
+class ChangePasswordRequest(BaseModel):
+    """修改密码请求"""
+    old_password: str
+    new_password: str = Field(..., min_length=6, max_length=128)
+
+
+# ===== 响应 =====
+
+class UserResponse(BaseModel):
+    """用户信息响应"""
+    id: str
+    email: Optional[str] = None
+    phone: Optional[str] = None
+    name: str
+    avatar: Optional[str] = None
+    role: UserRole
+    is_verified: bool
+
+    # 根据角色返回对应的组织 ID
+    brand_id: Optional[str] = None
+    agency_id: Optional[str] = None
+    creator_id: Optional[str] = None
+
+    # 当前所属租户（品牌方）- 用于数据隔离
+    tenant_id: Optional[str] = None
+    tenant_name: Optional[str] = None
+
+    class Config:
+        from_attributes = True
+
+
+class TokenResponse(BaseModel):
+    """Token 响应"""
+    access_token: str
+    refresh_token: str
+    token_type: str = "bearer"
+    expires_in: int = 900  # 15 分钟 = 900 秒
+
+
+class LoginResponse(BaseModel):
+    """登录响应"""
+    access_token: str
+    refresh_token: str
+    token_type: str = "bearer"
+    expires_in: int = 900
+    user: UserResponse
+
+
+class RefreshTokenResponse(BaseModel):
+    """刷新 Token 响应"""
+    access_token: str
+    token_type: str = "bearer"
+    expires_in: int = 900