feat(antigravity): 添加 models 端点支持

- /antigravity/models: 返回全部模型（Claude + Gemini）
- /antigravity/v1/models: 返回全部模型（Claude API 格式）
- /antigravity/v1beta/models: 仅返回 Gemini 模型（v1beta 格式）

统一管理 antigravity 模型定义，避免重复代码

backend/internal/handler/gateway_handler.go

@@ -11,6 +11,7 @@ import (
 	"strings"
 	"time"
 
+	"github.com/Wei-Shaw/sub2api/internal/pkg/antigravity"
 	"github.com/Wei-Shaw/sub2api/internal/pkg/claude"
 	"github.com/Wei-Shaw/sub2api/internal/pkg/openai"
 	middleware2 "github.com/Wei-Shaw/sub2api/internal/server/middleware"
@@ -308,10 +309,21 @@ func (h *GatewayHandler) Messages(c *gin.Context) {
 
 // Models handles listing available models
 // GET /v1/models
-// Returns different model lists based on the API key's group platform
+// Returns different model lists based on the API key's group platform or forced platform
 func (h *GatewayHandler) Models(c *gin.Context) {
 	apiKey, _ := middleware2.GetApiKeyFromContext(c)
 
+	// 优先检查强制平台（/antigravity 路由）
+	if forcePlatform, ok := middleware2.GetForcePlatformFromContext(c); ok {
+		if forcePlatform == service.PlatformAntigravity {
+			c.JSON(http.StatusOK, gin.H{
+				"object": "list",
+				"data":   antigravity.DefaultModels(),
+			})
+			return
+		}
+	}
+
 	// Return OpenAI models for OpenAI platform groups
 	if apiKey != nil && apiKey.Group != nil && apiKey.Group.Platform == "openai" {
 		c.JSON(http.StatusOK, gin.H{
@@ -328,6 +340,15 @@ func (h *GatewayHandler) Models(c *gin.Context) {
 	})
 }
 
+// AntigravityModels 返回 Antigravity 支持的全部模型
+// GET /antigravity/models
+func (h *GatewayHandler) AntigravityModels(c *gin.Context) {
+	c.JSON(http.StatusOK, gin.H{
+		"object": "list",
+		"data":   antigravity.DefaultModels(),
+	})
+}
+
 // Usage handles getting account balance for CC Switch integration
 // GET /v1/usage
 func (h *GatewayHandler) Usage(c *gin.Context) {

backend/internal/handler/gemini_v1beta_handler.go

@@ -9,6 +9,7 @@ import (
 	"strings"
 	"time"
 
+	"github.com/Wei-Shaw/sub2api/internal/pkg/antigravity"
 	"github.com/Wei-Shaw/sub2api/internal/pkg/gemini"
 	"github.com/Wei-Shaw/sub2api/internal/pkg/googleapi"
 	"github.com/Wei-Shaw/sub2api/internal/server/middleware"
@@ -32,9 +33,9 @@ func (h *GatewayHandler) GeminiV1BetaListModels(c *gin.Context) {
 		return
 	}
 
-	// 强制 antigravity 模式：直接返回静态模型列表
+	// 强制 antigravity 模式：返回 antigravity 支持的模型列表
 	if forcePlatform == service.PlatformAntigravity {
-		c.JSON(http.StatusOK, gemini.FallbackModelsList())
+		c.JSON(http.StatusOK, antigravity.FallbackGeminiModelsList())
 		return
 	}
 
@@ -84,9 +85,9 @@ func (h *GatewayHandler) GeminiV1BetaGetModel(c *gin.Context) {
 		return
 	}
 
-	// 强制 antigravity 模式：直接返回静态模型信息
+	// 强制 antigravity 模式：返回 antigravity 模型信息
 	if forcePlatform == service.PlatformAntigravity {
-		c.JSON(http.StatusOK, gemini.FallbackModel(modelName))
+		c.JSON(http.StatusOK, antigravity.FallbackGeminiModel(modelName))
 		return
 	}