Migrated the add-on to Manifest V3 structure.

Key changes in this version:
- Registered a background event page (scripts) for Firefox compatibility alongside the service worker fallback.
- Added storage-based caching (using chrome.storage.local) to cache repository license details. This prevents redundant API requests and avoids hitting unauthenticated rate limits.
- Implemented a fast-path DOM scraper that parses the repository sidebar to inject the license badge instantly.
- Added dynamic page navigation support (attaching to Turbo and PJAX load/render events) to ensure the badge updates when clicking links inside GitHub without refreshing the page.
- Configured dynamic CSS styling using GitHub's native style variables, supporting Light, Dark, and Dimmed modes automatically.
- Integrated the complex license warning alert to display when custom exceptions or third-party license directories are present.