Switch init-template to use appkit repo template

Instead of using the CLI's embedded appkit template (which is out of sync
with the SDK), use the template from https://github.com/databricks/appkit.

This fixes the getRequestContext API mismatch issue where generated apps
use an API that doesn't exist in the @databricks/appkit SDK.

See: #4339
Depends on: databricks/appkit#60

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: keugenek

experimental/aitools/cmd/init_template/app.go

@@ -16,9 +16,9 @@ import (
 )
 
 const (
-	defaultTemplateRepo = "https://github.com/databricks/cli"
-	defaultTemplateDir  = "experimental/aitools/templates/appkit"
-	defaultBranch       = "main"
+	defaultTemplateRepo = "https://github.com/databricks/appkit"
+	defaultTemplateDir  = ""
+	defaultBranch       = "add-dab-template-schema" // TODO: change to "main" after PR #60 is merged
 	templatePathEnvVar  = "DATABRICKS_APPKIT_TEMPLATE_PATH"
 )