Improve editor and cookie-consent test coverage, fix RegExp.exec lint

- Add 5 editor tests: toolbar mousedown, _sync, exec with/without value
- Mock document.execCommand for happy-dom compatibility
- Add cookie-consent test for duplicate script guard
- Use RegExp.exec() instead of String.match() per ESLint rule

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

assets/modules/cookie-consent.js

@@ -2,7 +2,7 @@ const COOKIE_NAME = 'e_ticket_consent'
 const COOKIE_DAYS = 365
 
 function getCookie(name) {
-    const match = document.cookie.match(new RegExp('(^| )' + name + '=([^;]+)'))
+    const match = new RegExp('(^| )' + name + '=([^;]+)').exec(document.cookie)
 
     return match ? match[2] : null
 }