fix(composite): support CN providers

Extend composite routing, pricing, migrations, and admin options for Kimi, GLM, and DeepSeek.

backend/internal/handler/admin/group_handler.go

@@ -234,7 +234,7 @@ type UpdateGroupRequest struct {
 type CompositeRouteRequest struct {
 	PublicModel    string `json:"public_model" binding:"required"`
 	MatchType      string `json:"match_type" binding:"omitempty,oneof=exact prefix"`
-	TargetPlatform string `json:"target_platform" binding:"required,oneof=anthropic openai gemini antigravity grok"`
+	TargetPlatform string `json:"target_platform" binding:"required,oneof=anthropic openai gemini antigravity grok kimi zhipu deepseek"`
 	UpstreamModel  string `json:"upstream_model"`
 	Endpoint       string `json:"endpoint" binding:"omitempty,oneof=any messages count_tokens responses chat_completions embeddings images gemini"`
 	Priority       int    `json:"priority"`

backend/internal/handler/admin/group_handler_platform_test.go

@@ -71,13 +71,11 @@ func TestGroupPlatformBinding_RejectsInvalidPlatforms(t *testing.T) {
 	}
 }
 
-// 守住 composite 路由目标不放行 CN:CN 平台不可作为 composite 路由目标
-// （DetectModelPlatform/isConcreteRequestPlatform 均无 CN 分支,放行即打开半实现路径）。
-func TestCompositeRouteTargetPlatform_StillExcludesCNProviders(t *testing.T) {
+func TestCompositeRouteTargetPlatform_AllowsCNProviders(t *testing.T) {
 	for _, platform := range []string{"kimi", "zhipu", "deepseek"} {
 		var req CompositeRouteRequest
 		body := fmt.Sprintf(`{"public_model":"m","target_platform":%q}`, platform)
-		require.Error(t, bindGroupPlatformJSON(t, &req, body),
-			"composite target_platform %q 应保持被拒", platform)
+		require.NoError(t, bindGroupPlatformJSON(t, &req, body))
+		require.Equal(t, platform, req.TargetPlatform)
 	}
 }