chore: Rename project from WebTriviasMulti to Trivy

- Update all code references to new name
- Rename design document
- Update package.json
- Update frontend titles and branding

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

frontend/package.json

@@ -1,5 +1,5 @@
 {
-  "name": "webtriviasmulti-frontend",
+  "name": "trivy-frontend",
   "private": true,
   "version": "1.0.0",
   "type": "module",