Refactor to Promise-based APIs

[google-labs-jules]

Refactored the browser extension codebase to exclusively use Promise-based APIs and async/await syntax, removing all legacy callback support.

Key changes:

• Updated interface/lib/browserDetector.js to prioritize window.browser and remove legacy promise support checks.
• Refactored interface/lib/genericCookieHandler.js to return Promises and use async/await for cookie operations.
• Refactored interface/lib/genericStorageHandler.js to simplify getLocal and setLocal using Promises.
• Updated interface/lib/optionsHandler.js and interface/devtools/permissionHandler.js to use Promises for messaging.
• Refactored interface/popup/cookieHandlerPopup.js and interface/devtools/cookieHandlerDevtools.js to use Promises.
• Updated callers in interface/popup/cookie-list.js and interface/options/options.js to use await/async.
• Refactored cookie-editor.js (background script) to use Promises.

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PR created automatically by Jules for task 8975195924216469546 started by @Moustachauve

[google-labs-jules]

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