Build the embedded admin UI from CyberCoveLLC/threshold-ui

- internal/ui/VERSION pins the threshold-ui commit
- scripts/uiupdate.sh and scripts/build-ui.sh clone
  https://repo.anhonesthost.net/CyberCoveLLC/threshold-ui.git; the
  GitHub artifact download path (hashicorp/boundary-ui) is removed
- clone/embed directory renamed .tmp/boundary-ui -> .tmp/threshold-ui
  (Makefile, assets.go, .github build.yml paths)

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

scripts/uiupdate.sh

@@ -13,14 +13,9 @@ if [ -z "$UI_COMMITISH" ]; then
 	echo "Must set UI_COMMITISH"; exit 1
 fi
 
-UI_EDITION=$(make --no-print-directory edition)
-
-if [ "$UI_EDITION" == "oss" ]; then
-  UI_REPO=https://github.com/hashicorp/boundary-ui
-else
-  UI_VERSION_FILE="${UI_VERSION_FILE}_ent"
-  UI_REPO=https://github.com/hashicorp/boundary-ui-enterprise
-fi
+# Threshold ships a single (community) edition of the admin UI, built from the
+# CyberCoveLLC/threshold-ui fork of hashicorp/boundary-ui.
+UI_REPO=${UI_REPO:-https://repo.anhonesthost.net/CyberCoveLLC/threshold-ui.git}
 
 shafileabs="$(pwd)/${UI_VERSION_FILE}"
 V="$(git ls-remote ${UI_REPO} ${UI_COMMITISH})"