Migrate extension to Manifest V3 and follow Chrome extension best practices

[bubach]

Migrated the AdfreePlay Chrome extension from Manifest V2 to Manifest V3. Replaced deprecated background scripts with a background service worker, updated extension action APIs, replaced chrome.tabs.getSelected and executeScript, added chrome.storage.local state persistence, modernized JS syntax, and added automated verification tests.

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PR created automatically by Jules for task 1707401705406270917 started by @bubach

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