Update to Manifest V3: Migrate Chrome extension to modern APIs

[Copilot]

This PR migrates the Org Capture extension from Chrome Manifest V2 to Manifest V3, ensuring compatibility with modern Chrome browsers and future-proofing the extension.

Changes Made

manifest.json

• Updated manifest_version from 2 to 3
• Replaced background.scripts with background.service_worker pointing to background.js
• Changed browser_action to action (new V3 terminology)
• Added "scripting" permission required for the new script injection API
• Updated command from _execute_browser_action to _execute_action

background.js

• Replaced deprecated chrome.browserAction.onClicked with chrome.action.onClicked
• Updated script injection from chrome.tabs.executeScript() to chrome.scripting.executeScript() with new target-based API structure

Compatibility

All existing functionality is preserved:

• The extension continues to capture web pages and send them to Emacs via org-protocol
• Options page and storage functionality remain unchanged (using V3-compatible chrome.storage API)
• Keyboard shortcuts and user interface behavior are identical
• All configuration options work as before

Testing

• ✅ Manifest syntax validation passes
• ✅ All JavaScript files have valid syntax
• ✅ Extension file structure is complete
• ✅ Chrome APIs used in content scripts are V3-compatible

This migration addresses Chrome's deprecation of Manifest V2 and ensures the extension will continue working in future Chrome versions that require Manifest V3.

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