fix(snapshot): allow same-name in pre-task check for update

The pre-task validation in apiSnapshotsUpdate was incorrectly rejecting
PUT requests that set the Name to the snapshot's current name. This caused
a 409 response before creating a task, which broke the system test
SnapshotsAPITestCreateUpdate that expects a task to be created and then
fail inside the task.

The fix restores the 'b.Name != name' condition in the pre-task check so
that same-name updates pass through to the task, where the in-task
duplicate check will properly fail them (returning a failed task state
instead of a direct 409).

api/snapshot.go

@@ -339,8 +339,8 @@ func apiSnapshotsUpdate(c *gin.Context) {
 		return
 	}
 
-	// Pre-task validation of new name if provided
-	if b.Name != "" {
+	// Pre-task validation of new name if provided (skip if renaming to same name)
+	if b.Name != "" && b.Name != name {
 		_, err = collection.ByName(b.Name)
 		if err == nil {
 			AbortWithJSONError(c, 409, fmt.Errorf("unable to rename: snapshot %s already exists", b.Name))