Fix UUID cast in task creation, add kind test manifests

- Fix parent_task_id NULLIF cast to UUID type in INSERT query
- Fix itoa helper to use strconv.Itoa
- Handle AddReaction errors gracefully in webhook handler
- Add hack/kind/ manifests for local testing with kind cluster

hack/kind/manifests/namespace.yaml

@@ -0,0 +1,5 @@
+---
+apiVersion: v1
+kind: Namespace
+metadata:
+  name: forgebot