fix(user,customer): return 409 on phone duplicate-key races

Map E11000 from the per-collection phone index to friendly conflict
errors and skip redundant GetByPhone when the phone is unchanged.

Not blocking: IAT test DB may need a one-off dedupe for index build;
phone uniqueness is per collection (users vs customers), not global.

internal/user/handler.go

@@ -170,6 +170,9 @@ func (h *Handler) UpdateProfile(c echo.Context) error {
 
 	user, err := h.service.Update(c.Request().Context(), userID, form)
 	if err != nil {
+		if isUserConflictError(err) {
+			return response.Conflict(c, err.Error())
+		}
 		return response.BadRequest(c, err.Error(), "")
 	}
 
@@ -274,6 +277,9 @@ func (h *Handler) CreateUser(c echo.Context) error {
 	// Call service
 	user, err := h.service.Register(c.Request().Context(), form)
 	if err != nil {
+		if isUserConflictError(err) {
+			return response.Conflict(c, err.Error())
+		}
 		return response.BadRequest(c, err.Error(), "")
 	}
 
@@ -386,6 +392,9 @@ func (h *Handler) UpdateUser(c echo.Context) error {
 	// Call service
 	user, err := h.service.Update(c.Request().Context(), idStr, form)
 	if err != nil {
+		if isUserConflictError(err) {
+			return response.Conflict(c, err.Error())
+		}
 		return response.BadRequest(c, err.Error(), "")
 	}