Migrate browser extension to Manifest V3

[Copilot]

This PR migrates the pbkit-devtools browser extension from Manifest V2 to Manifest V3, in preparation for Chrome's deprecation of Manifest V2 (see Chrome's Manifest V3 migration guide).

Changes Made

The migration updates packages/browser-extension/template/manifest.json with the following changes:

1. Updated manifest version: Changed manifest_version from 2 to 3

2. Converted background script to service worker: Replaced the background.scripts array with background.service_worker to use the new service worker-based background script model:

   - "background": {
   -   "scripts": ["background.js"]
   - }
   + "background": {
   +   "service_worker": "background.js"
   + }

3. Added host permissions: Added host_permissions field to explicitly declare URL access permissions that were previously implicit in the content scripts matches:

   "host_permissions": ["<all_urls>"]

Compatibility Verification

• background.js: Already fully compatible with service workers. It only uses:

  • chrome.runtime.onConnect API (fully supported in service workers)
  • Standard JavaScript (WeakMap, objects, functions)
  • No DOM access or other service worker-incompatible APIs

• content-script.js: Remains fully compatible with Manifest V3:

  • Uses chrome.runtime.connect which is unchanged in MV3
  • Message passing functionality works identically

The extension is now compliant with Manifest V3 requirements and will continue to work as Chrome phases out Manifest V2 support.

Fixes #1

Original prompt

---

This section details on the original issue you should resolve

<issue_title>migrate to manifest v3</issue_title>
<issue_description>https://developer.chrome.com/docs/extensions/mv3/intro/mv3-migration/
</issue_description>

Comments on the Issue (you are @copilot in this section)

Fixes #12

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