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

internal/database/tasks.go

@@ -2,6 +2,7 @@ package database
 
 import (
 	"context"
+	"strconv"
 	"time"
 
 	"github.com/jackc/pgx/v5"
@@ -35,7 +36,7 @@ func (db *DB) CreateTask(ctx context.Context, req models.CreateTaskRequest) (*mo
 			issue_number, pr_number, comment_id, body, author,
 			extra_tools, pool_ref
 		) VALUES (
-			NULLIF($1, ''), $2, $3, $4, $5,
+			NULLIF($1, '')::uuid, $2, $3, $4, $5,
 			$6, $7, $8, $9, $10,
 			$11, $12
 		) RETURNING id, created_at`,
@@ -173,5 +174,5 @@ func scanTasks(rows pgx.Rows) ([]models.Task, error) {
 }
 
 func itoa(i int) string {
-	return string(rune('0'+i)) + ""
+	return strconv.Itoa(i)
 }