refactor(architecture): eliminate internal package and complete cordis single-owner model and repository migration

- Physically purged all legacy internal/ packages, centralized pkg/model/ and pkg/repository/
- Migrated domain models and database repositories into self-contained owner plugins (user, auth, message_gateway, admin, upload, risk_control)
- Decoupled cross-plugin interactions via pure core/contracts and typed EventBus
- Ensured 100% test coverage pass, zero data races (-race clean), and 0 lint issues in make code-check

plugins/domain/message_gateway/admin_handlers.go

@@ -7,7 +7,7 @@ import (
 	"net/http"
 	"strconv"
 
-	"github.com/Rain-kl/Wavelet/internal/shared/response"
+	"github.com/Rain-kl/Wavelet/pkg/response"
 	"github.com/gin-gonic/gin"
 )
 
@@ -20,7 +20,7 @@ import (
 // @Success 200 {object} response.Any{data=[]Definition}
 // @Router /api/v1/admin/message-gateway/channels/definitions [get]
 func ListAdminChannelDefinitions(c *gin.Context) {
-	c.JSON(http.StatusOK, response.OK(channelDefinitions()))
+	c.JSON(http.StatusOK, response.OK(listDefinitions()))
 }
 
 // ListAdminChannels lists configured messaging channels with secrets masked.