feat(backend): 完善 Gemini OAuth Token 处理

- 修复 account_handler 中 token 字段类型转换（int64 转 string）
- 增强 Account.GetCredential 支持多种数值类型（float64, int, json.Number 等）
- 添加 Account.IsGemini() 方法用于平台判断
- 优化 refresh_token 和 scope 的空值处理

backend/internal/handler/admin/account_handler.go

@@ -2,6 +2,7 @@ package admin
 
 import (
 	"strconv"
+	"strings"
 
 	"github.com/Wei-Shaw/sub2api/internal/model"
 	"github.com/Wei-Shaw/sub2api/internal/pkg/claude"
@@ -375,18 +376,22 @@ func (h *AccountHandler) Refresh(c *gin.Context) {
 			newCredentials[k] = v
 		}
 
-		// Update token-related fields
-		newCredentials["access_token"] = tokenInfo.AccessToken
-		newCredentials["token_type"] = tokenInfo.TokenType
-		newCredentials["expires_in"] = tokenInfo.ExpiresIn
-		newCredentials["expires_at"] = tokenInfo.ExpiresAt
-		newCredentials["refresh_token"] = tokenInfo.RefreshToken
-		newCredentials["scope"] = tokenInfo.Scope
-	}
+			// Update token-related fields
+			newCredentials["access_token"] = tokenInfo.AccessToken
+			newCredentials["token_type"] = tokenInfo.TokenType
+			newCredentials["expires_in"] = strconv.FormatInt(tokenInfo.ExpiresIn, 10)
+			newCredentials["expires_at"] = strconv.FormatInt(tokenInfo.ExpiresAt, 10)
+			if strings.TrimSpace(tokenInfo.RefreshToken) != "" {
+				newCredentials["refresh_token"] = tokenInfo.RefreshToken
+			}
+			if strings.TrimSpace(tokenInfo.Scope) != "" {
+				newCredentials["scope"] = tokenInfo.Scope
+			}
+		}
 
-	updatedAccount, err := h.adminService.UpdateAccount(c.Request.Context(), accountID, &service.UpdateAccountInput{
-		Credentials: newCredentials,
-	})
+		updatedAccount, err := h.adminService.UpdateAccount(c.Request.Context(), accountID, &service.UpdateAccountInput{
+			Credentials: newCredentials,
+		})
 	if err != nil {
 		response.ErrorFrom(c, err)
 		return

backend/internal/model/account.go

@@ -4,6 +4,7 @@ import (
 	"database/sql/driver"
 	"encoding/json"
 	"errors"
+	"strconv"
 	"time"
 
 	"gorm.io/gorm"
@@ -128,8 +129,37 @@ func (a *Account) GetCredential(key string) string {
 		return ""
 	}
 	if v, ok := a.Credentials[key]; ok {
-		if s, ok := v.(string); ok {
-			return s
+		switch vv := v.(type) {
+		case string:
+			return vv
+		case json.Number:
+			return vv.String()
+		case float64:
+			// JSON numbers decode to float64; keep integer formatting for integer-like values.
+			i := int64(vv)
+			if vv == float64(i) {
+				return strconv.FormatInt(i, 10)
+			}
+			return strconv.FormatFloat(vv, 'f', -1, 64)
+		case float32:
+			f := float64(vv)
+			i := int64(f)
+			if f == float64(i) {
+				return strconv.FormatInt(i, 10)
+			}
+			return strconv.FormatFloat(f, 'f', -1, 64)
+		case int:
+			return strconv.FormatInt(int64(vv), 10)
+		case int64:
+			return strconv.FormatInt(vv, 10)
+		case int32:
+			return strconv.FormatInt(int64(vv), 10)
+		case uint:
+			return strconv.FormatUint(uint64(vv), 10)
+		case uint64:
+			return strconv.FormatUint(vv, 10)
+		case uint32:
+			return strconv.FormatUint(uint64(vv), 10)
 		}
 	}
 	return ""
@@ -291,6 +321,11 @@ func (a *Account) IsAnthropic() bool {
 	return a.Platform == PlatformAnthropic
 }
 
+// IsGemini 检查是否为 Gemini 平台账号
+func (a *Account) IsGemini() bool {
+	return a.Platform == PlatformGemini
+}
+
 // IsOpenAIOAuth 检查是否为 OpenAI OAuth 类型账号
 func (a *Account) IsOpenAIOAuth() bool {
 	return a.IsOpenAI() && a.Type == AccountTypeOAuth

backend/internal/service/gemini_oauth_service.go

@@ -139,7 +139,8 @@ func (s *GeminiOAuthService) ExchangeCode(ctx context.Context, input *GeminiExch
 	}
 	s.sessionStore.Delete(input.SessionID)
 
-	expiresAt := time.Now().Unix() + tokenResp.ExpiresIn
+	// 计算过期时间时减去 5 分钟安全时间窗口,考虑网络延迟和时钟偏差
+	expiresAt := time.Now().Unix() + tokenResp.ExpiresIn - 300
 	projectID, _ := s.fetchProjectID(ctx, tokenResp.AccessToken, proxyURL)
 
 	return &GeminiTokenInfo{
@@ -167,7 +168,8 @@ func (s *GeminiOAuthService) RefreshToken(ctx context.Context, refreshToken, pro
 
 		tokenResp, err := s.oauthClient.RefreshToken(ctx, refreshToken, proxyURL)
 		if err == nil {
-			expiresAt := time.Now().Unix() + tokenResp.ExpiresIn
+			// 计算过期时间时减去 5 分钟安全时间窗口,考虑网络延迟和时钟偏差
+			expiresAt := time.Now().Unix() + tokenResp.ExpiresIn - 300
 			return &GeminiTokenInfo{
 				AccessToken:  tokenResp.AccessToken,
 				RefreshToken: tokenResp.RefreshToken,