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/template/routers.go

@@ -10,7 +10,7 @@ import (
 	"github.com/gin-gonic/gin"
 	"gorm.io/gorm"
 
-	"github.com/Rain-kl/Wavelet/internal/common/response"
+	"github.com/Rain-kl/Wavelet/internal/shared/response"
 )
 
 // CreateTemplateRequest 创建模板请求

internal/apps/admin/template/routers_test.go

@@ -15,7 +15,7 @@ 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 {