Migrate Chrome extension to Manifest V3

[arkanovicz]

Chrome 139+ no longer supports Manifest V2 extensions. This commit updates TabFS to use Manifest V3 for Chrome compatibility.

Changes:

• manifest.json: Update to manifest_version 3

  • Move <all_urls> from permissions to host_permissions
  • Add "scripting" permission for chrome.scripting API
  • Replace background scripts with service_worker
  • Remove deprecated content_security_policy format

• background.js: Adapt for MV3 service worker environment

  • Replace browser.tabs.executeScript with chrome.scripting.executeScript
  • Add executeScript() helper that uses eval in MAIN world context
  • Replace window.Routes with globalThis.Routes for service worker
  • Replace window.fetch with fetch (service workers have fetch natively)
  • Add browser shim (const browser = globalThis.browser || chrome)

Notes:

• Native messaging keeps service worker alive (Chrome 100+)
• Firefox users can continue using MV2 (Firefox doesn't deprecate MV2)
• The eval-based script execution maintains compatibility with TabFS's dynamic code execution features (evals/, watches/, inputs/)

Note: this must be carefully reviewed, most changes were performed by a coding agent.