Migrate the extension to Manifest V3

[InventivetalentDev]

Manifest:

• manifest_version 3, browser_action -> action
• persistent background page -> background.service_worker
• host permissions (<all_urls>, http:///, https:///) moved to
  host_permissions; added "scripting" for the popup's injection
• content_security_policy is now an object. MV3 forbids remote script
  sources, so the remote-sli.de/cdnjs/jquery/google-analytics entries are
  gone and the policy is the MV3 default
• web_accessible_resources entries carry the now-required "matches"

Background page -> service worker (background.js):

• imports sessionGrabber.js via importScripts; jQuery is dropped from the
  worker ($.extend -> Object.assign) since it needs a DOM
• resizeImage() has no DOM to work with, so it decodes the capture with
  createImageBitmap and scales it on an OffscreenCanvas, then serialises
  through FileReader. Output is unchanged: a 40%-scale PNG payload with
  the data URL header stripped
• chrome.browserAction -> chrome.action
• chrome.tabs.getSelected is gone; the badge now targets sender.tab (the
  tab the controller actually runs in) and falls back to the active tab
• takeScreenshot() is promise-based and reports failures instead of
  leaving the caller waiting on a response that never comes

Popup (index.js):

• chrome.tabs.getSelected -> chrome.tabs.query, via a withActiveTab helper
• chrome.tabs.executeScript -> chrome.scripting.executeScript. MV3 has no
  {code: ...}, so remote_slide is handed over with func/args, and the
  injections are chained so pageController.js only runs once jQuery and
  socket.io are in place
• chrome.extension.onMessage -> chrome.runtime.onMessage
• chrome.browserAction -> chrome.action, and the badge calls now use the
  stored controlledTab id instead of a non-existent .id on that number

Content scripts:

• chrome.extension.onMessage/getURL -> chrome.runtime equivalents in
  injector.js and preziInjector.js

Other:

• util/mv3-compat.js restores chrome.extension.onMessage/sendMessage/getURL
  for the bundled inject/controller submodule, which still targets MV2. It
  is injected just before pageController.js and can be removed once that
  submodule is migrated
• lib/analytics.js loaded ga.js from a remote origin, which MV3 does not
  allow; removed along with its script tag

Co-Authored-By: Claude noreply@anthropic.com
Claude-Session: https://claude.ai/code/session_01TwwH67Z38ZV9GaWAtPZhfP