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>

.github/workflows/build.yml

@@ -170,7 +170,7 @@ jobs:
           commit: ${{ steps.set-sha.outputs.sha }}
           repo: "hashicorp/boundary-ui"
           name: admin-ui-${{ needs.product-metadata.outputs.product-edition }}
-          path: internal/ui/.tmp/boundary-ui/ui/admin/dist
+          path: internal/ui/.tmp/threshold-ui/ui/admin/dist
       - name: Go Build
         env:
           CGO_ENABLED: "0"
@@ -246,7 +246,7 @@ jobs:
           commit: ${{ steps.set-sha.outputs.sha }}
           repo: "hashicorp/boundary-ui"
           name: admin-ui-${{ needs.product-metadata.outputs.product-edition }}
-          path: internal/ui/.tmp/boundary-ui/ui/admin/dist
+          path: internal/ui/.tmp/threshold-ui/ui/admin/dist
       - name: Go Build
         env:
           CGO_ENABLED: "0"
@@ -345,7 +345,7 @@ jobs:
           commit: ${{ steps.set-sha.outputs.sha }}
           repo: "hashicorp/boundary-ui"
           name: admin-ui-${{ needs.product-metadata.outputs.product-edition }}
-          path: internal/ui/.tmp/boundary-ui/ui/admin/dist
+          path: internal/ui/.tmp/threshold-ui/ui/admin/dist
       - name: Go Build
         env:
           CGO_ENABLED: "0"