fix(store): return ErrRecordNotFound when updating non-existent template

RowsAffected == 0 now returns gorm.ErrRecordNotFound so the handler can respond with 404 instead of silently returning 200.

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

internal/handler/template.go

@@ -1,6 +1,7 @@
 package handler
 
 import (
+	"errors"
 	"strconv"
 
 	"gcy_hpc_server/internal/model"
@@ -9,6 +10,7 @@ import (
 
 	"github.com/gin-gonic/gin"
 	"go.uber.org/zap"
+	"gorm.io/gorm"
 )
 
 type TemplateHandler struct {
@@ -111,8 +113,13 @@ func (h *TemplateHandler) UpdateTemplate(c *gin.Context) {
 	}
 
 	if err := h.store.Update(c.Request.Context(), id, &req); err != nil {
+		if errors.Is(err, gorm.ErrRecordNotFound) {
+			h.logger.Warn("template not found for update", zap.Int64("id", id))
+			server.NotFound(c, "template not found")
+			return
+		}
 		h.logger.Error("failed to update template", zap.Int64("id", id), zap.Error(err))
-		server.InternalError(c, err.Error())
+		server.InternalError(c, "failed to update template")
 		return
 	}