feat(auth): 实现 TOTP 双因素认证功能

新增功能：
- 支持 Google Authenticator 等应用进行 TOTP 二次验证
- 用户可在个人设置中启用/禁用 2FA
- 登录时支持 TOTP 验证流程
- 管理后台可全局开关 TOTP 功能

安全增强：
- TOTP 密钥使用 AES-256-GCM 加密存储
- 添加 TOTP_ENCRYPTION_KEY 配置项，必须手动配置才能启用功能
- 防止服务重启导致加密密钥变更使用户无法登录
- 验证失败次数限制，防止暴力破解

配置说明：
- Docker 部署：在 .env 中设置 TOTP_ENCRYPTION_KEY
- 非 Docker 部署：在 config.yaml 中设置 totp.encryption_key
- 生成密钥命令：openssl rand -hex 32

backend/ent/user_update.go

@@ -187,6 +187,60 @@ func (_u *UserUpdate) SetNillableNotes(v *string) *UserUpdate {
 	return _u
 }
 
+// SetTotpSecretEncrypted sets the "totp_secret_encrypted" field.
+func (_u *UserUpdate) SetTotpSecretEncrypted(v string) *UserUpdate {
+	_u.mutation.SetTotpSecretEncrypted(v)
+	return _u
+}
+
+// SetNillableTotpSecretEncrypted sets the "totp_secret_encrypted" field if the given value is not nil.
+func (_u *UserUpdate) SetNillableTotpSecretEncrypted(v *string) *UserUpdate {
+	if v != nil {
+		_u.SetTotpSecretEncrypted(*v)
+	}
+	return _u
+}
+
+// ClearTotpSecretEncrypted clears the value of the "totp_secret_encrypted" field.
+func (_u *UserUpdate) ClearTotpSecretEncrypted() *UserUpdate {
+	_u.mutation.ClearTotpSecretEncrypted()
+	return _u
+}
+
+// SetTotpEnabled sets the "totp_enabled" field.
+func (_u *UserUpdate) SetTotpEnabled(v bool) *UserUpdate {
+	_u.mutation.SetTotpEnabled(v)
+	return _u
+}
+
+// SetNillableTotpEnabled sets the "totp_enabled" field if the given value is not nil.
+func (_u *UserUpdate) SetNillableTotpEnabled(v *bool) *UserUpdate {
+	if v != nil {
+		_u.SetTotpEnabled(*v)
+	}
+	return _u
+}
+
+// SetTotpEnabledAt sets the "totp_enabled_at" field.
+func (_u *UserUpdate) SetTotpEnabledAt(v time.Time) *UserUpdate {
+	_u.mutation.SetTotpEnabledAt(v)
+	return _u
+}
+
+// SetNillableTotpEnabledAt sets the "totp_enabled_at" field if the given value is not nil.
+func (_u *UserUpdate) SetNillableTotpEnabledAt(v *time.Time) *UserUpdate {
+	if v != nil {
+		_u.SetTotpEnabledAt(*v)
+	}
+	return _u
+}
+
+// ClearTotpEnabledAt clears the value of the "totp_enabled_at" field.
+func (_u *UserUpdate) ClearTotpEnabledAt() *UserUpdate {
+	_u.mutation.ClearTotpEnabledAt()
+	return _u
+}
+
 // AddAPIKeyIDs adds the "api_keys" edge to the APIKey entity by IDs.
 func (_u *UserUpdate) AddAPIKeyIDs(ids ...int64) *UserUpdate {
 	_u.mutation.AddAPIKeyIDs(ids...)
@@ -603,6 +657,21 @@ func (_u *UserUpdate) sqlSave(ctx context.Context) (_node int, err error) {
 	if value, ok := _u.mutation.Notes(); ok {
 		_spec.SetField(user.FieldNotes, field.TypeString, value)
 	}
+	if value, ok := _u.mutation.TotpSecretEncrypted(); ok {
+		_spec.SetField(user.FieldTotpSecretEncrypted, field.TypeString, value)
+	}
+	if _u.mutation.TotpSecretEncryptedCleared() {
+		_spec.ClearField(user.FieldTotpSecretEncrypted, field.TypeString)
+	}
+	if value, ok := _u.mutation.TotpEnabled(); ok {
+		_spec.SetField(user.FieldTotpEnabled, field.TypeBool, value)
+	}
+	if value, ok := _u.mutation.TotpEnabledAt(); ok {
+		_spec.SetField(user.FieldTotpEnabledAt, field.TypeTime, value)
+	}
+	if _u.mutation.TotpEnabledAtCleared() {
+		_spec.ClearField(user.FieldTotpEnabledAt, field.TypeTime)
+	}
 	if _u.mutation.APIKeysCleared() {
 		edge := &sqlgraph.EdgeSpec{
 			Rel:     sqlgraph.O2M,
@@ -1147,6 +1216,60 @@ func (_u *UserUpdateOne) SetNillableNotes(v *string) *UserUpdateOne {
 	return _u
 }
 
+// SetTotpSecretEncrypted sets the "totp_secret_encrypted" field.
+func (_u *UserUpdateOne) SetTotpSecretEncrypted(v string) *UserUpdateOne {
+	_u.mutation.SetTotpSecretEncrypted(v)
+	return _u
+}
+
+// SetNillableTotpSecretEncrypted sets the "totp_secret_encrypted" field if the given value is not nil.
+func (_u *UserUpdateOne) SetNillableTotpSecretEncrypted(v *string) *UserUpdateOne {
+	if v != nil {
+		_u.SetTotpSecretEncrypted(*v)
+	}
+	return _u
+}
+
+// ClearTotpSecretEncrypted clears the value of the "totp_secret_encrypted" field.
+func (_u *UserUpdateOne) ClearTotpSecretEncrypted() *UserUpdateOne {
+	_u.mutation.ClearTotpSecretEncrypted()
+	return _u
+}
+
+// SetTotpEnabled sets the "totp_enabled" field.
+func (_u *UserUpdateOne) SetTotpEnabled(v bool) *UserUpdateOne {
+	_u.mutation.SetTotpEnabled(v)
+	return _u
+}
+
+// SetNillableTotpEnabled sets the "totp_enabled" field if the given value is not nil.
+func (_u *UserUpdateOne) SetNillableTotpEnabled(v *bool) *UserUpdateOne {
+	if v != nil {
+		_u.SetTotpEnabled(*v)
+	}
+	return _u
+}
+
+// SetTotpEnabledAt sets the "totp_enabled_at" field.
+func (_u *UserUpdateOne) SetTotpEnabledAt(v time.Time) *UserUpdateOne {
+	_u.mutation.SetTotpEnabledAt(v)
+	return _u
+}
+
+// SetNillableTotpEnabledAt sets the "totp_enabled_at" field if the given value is not nil.
+func (_u *UserUpdateOne) SetNillableTotpEnabledAt(v *time.Time) *UserUpdateOne {
+	if v != nil {
+		_u.SetTotpEnabledAt(*v)
+	}
+	return _u
+}
+
+// ClearTotpEnabledAt clears the value of the "totp_enabled_at" field.
+func (_u *UserUpdateOne) ClearTotpEnabledAt() *UserUpdateOne {
+	_u.mutation.ClearTotpEnabledAt()
+	return _u
+}
+
 // AddAPIKeyIDs adds the "api_keys" edge to the APIKey entity by IDs.
 func (_u *UserUpdateOne) AddAPIKeyIDs(ids ...int64) *UserUpdateOne {
 	_u.mutation.AddAPIKeyIDs(ids...)
@@ -1593,6 +1716,21 @@ func (_u *UserUpdateOne) sqlSave(ctx context.Context) (_node *User, err error) {
 	if value, ok := _u.mutation.Notes(); ok {
 		_spec.SetField(user.FieldNotes, field.TypeString, value)
 	}
+	if value, ok := _u.mutation.TotpSecretEncrypted(); ok {
+		_spec.SetField(user.FieldTotpSecretEncrypted, field.TypeString, value)
+	}
+	if _u.mutation.TotpSecretEncryptedCleared() {
+		_spec.ClearField(user.FieldTotpSecretEncrypted, field.TypeString)
+	}
+	if value, ok := _u.mutation.TotpEnabled(); ok {
+		_spec.SetField(user.FieldTotpEnabled, field.TypeBool, value)
+	}
+	if value, ok := _u.mutation.TotpEnabledAt(); ok {
+		_spec.SetField(user.FieldTotpEnabledAt, field.TypeTime, value)
+	}
+	if _u.mutation.TotpEnabledAtCleared() {
+		_spec.ClearField(user.FieldTotpEnabledAt, field.TypeTime)
+	}
 	if _u.mutation.APIKeysCleared() {
 		edge := &sqlgraph.EdgeSpec{
 			Rel:     sqlgraph.O2M,