feat: 实现邮箱验证码注册/登录功能

- 后端: 新增验证码服务(生成/存储/验证)和邮件发送服务(开发环境控制台输出)
- 后端: 新增 POST /auth/send-code 端点，支持注册/登录/重置密码三种用途
- 后端: 注册流程要求邮箱验证码，验证通过后 is_verified=True
- 后端: 登录支持邮箱+密码 或 邮箱+验证码 两种方式
- 前端: 注册页增加验证码输入框和获取验证码按钮(60秒倒计时)
- 前端: 登录页增加密码登录/验证码登录双Tab切换
- 测试: conftest 添加 bypass_verification fixture，所有 367 测试通过

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/app/schemas/auth.py

@@ -8,13 +8,28 @@ from app.models.user import UserRole
 
 # ===== 请求 =====
 
+class SendEmailCodeRequest(BaseModel):
+    """发送邮箱验证码请求"""
+    email: EmailStr
+    purpose: str = Field("register", pattern=r"^(register|login|reset_password)$")
+
+    class Config:
+        json_schema_extra = {
+            "example": {
+                "email": "user@example.com",
+                "purpose": "register"
+            }
+        }
+
+
 class RegisterRequest(BaseModel):
     """注册请求"""
-    email: Optional[EmailStr] = None
+    email: EmailStr
     phone: Optional[str] = Field(None, pattern=r"^1[3-9]\d{9}$")
     password: str = Field(..., min_length=6, max_length=128)
     name: str = Field(..., min_length=1, max_length=100)
     role: UserRole
+    email_code: str = Field(..., min_length=4, max_length=8, description="邮箱验证码")
 
     class Config:
         json_schema_extra = {
@@ -22,17 +37,18 @@ class RegisterRequest(BaseModel):
                 "email": "user@example.com",
                 "password": "password123",
                 "name": "张三",
-                "role": "creator"
+                "role": "creator",
+                "email_code": "123456"
             }
         }
 
 
 class LoginRequest(BaseModel):
-    """登录请求（邮箱或手机号）"""
+    """登录请求（支持邮箱+密码 或 邮箱+验证码）"""
     email: Optional[EmailStr] = None
     phone: Optional[str] = None
     password: Optional[str] = None
-    sms_code: Optional[str] = None  # 短信验证码
+    email_code: Optional[str] = None  # 邮箱验证码
 
     class Config:
         json_schema_extra = {