feat: migrate to manifest v3

[ignatiusmb]

Extracted from #133

The Chrome Web Store no longer accepts Manifest V2 as stated from https://developer.chrome.com/docs/extensions/mv2/, this PR goes through the migration checklist and converts the extension to use V3 APIs.

Compatibility with Firefox is a bit tricky but doable, according to https://stackoverflow.com/a/75203925

• Chrome is not happy with background.scripts and insists on using background.service_worker
• Firefox doesn't support background.service_worker and wants background.scripts

Before publishing to Firefox, we'll just need to replace "service_worker": "background.js" with "scripts": ["background.js"]. I've tested the extension locally on Firefox by loading it as a temporary extension and it happily accepts the .zip file.

However, I'm getting "Missing host permission for the tab" error on Firefox, which doesn't seem to happen with Chromium based browsers. This will need to be investigated further later on, we may need to change or add upon the "activeTab" permissions with "tabs", but that would trigger a warning message during installation.

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Closes #68 - kit works out of the box
Closes #69 - should work but upgrade to svelte 4
Closes #72 - kit works without additional configuration
Closes #73 - should work with all chromium browsers
Closes #76 - should not be a problem now

Also,
Closes #70