Rebrand Boundary UI to Threshold; neutralize HashiCorp update/phone-home endpoints

- Product name, app id, installer names, translations, titles -> Threshold
- Desktop: look for threshold CLI first, then boundary; migrate legacy
  Boundary user-data dir; updater/release lookups disabled unless configured
- Remove HashiCorp/IBM logos and art (plain placeholder mark), GitHub
  release workflows and HashiCorp release metadata
- Add NOTICE and README 'About this fork'

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

addons/rose/package.json

@@ -1,9 +1,9 @@
 {
   "name": "rose",
   "version": "0.0.0",
-  "description": "Styles and components for Boundary.",
+  "description": "Styles and components for Threshold.",
   "license": "BUSL-1.1",
-  "author": "HashiCorp",
+  "author": "CyberCove LLC (fork of HashiCorp Boundary UI)",
   "keywords": [
     "ember-addon"
   ],