[ENGINEERING] Your issue title

[LC0229]

What is the issue?

• Create a new directory extension/ at repo root (or frontend/extension/ if preferred).
• Add manifest.json with Manifest V3: name, version, permissions (e.g. activeTab, storage, scripting, host permissions for target job sites).
• Add minimal background service worker (e.g. empty script that loads).
• Add placeholder popup.html + popup.js and optional popup.css.
• Document in README how to load the unpacked extension in Chrome (chrome://extensions → Load unpacked → select folder).

Additional context

• Acceptance criteria: Extension loads in Chrome without errors; popup opens when icon is clicked.