refactor(structure): group platform, infra, and shared packages

Reorganize internal packages into platform/infra/shared layers and update
imports, docs, and seed-count tests to match current system configs.

internal/apps/admin/auth_source/routers.go

@@ -16,7 +16,7 @@ import (
 	"github.com/Rain-kl/Wavelet/internal/repository"
 	"github.com/gin-gonic/gin"
 
-	"github.com/Rain-kl/Wavelet/internal/common/response"
+	"github.com/Rain-kl/Wavelet/internal/shared/response"
 )
 
 // AuthSourceRequest 创建或更新认证源的请求参数

internal/apps/admin/auth_source/routers_test.go

@@ -16,7 +16,7 @@ import (
 	"github.com/Rain-kl/Wavelet/internal/testhelper"
 	"github.com/gin-gonic/gin"
 
-	"github.com/Rain-kl/Wavelet/internal/common/response"
+	"github.com/Rain-kl/Wavelet/internal/shared/response"
 )
 
 func setupTestRouter(authUser *model.User) *gin.Engine {