Tab Sweep per nixcat.io

Initial Firefox release. A complete port of Zara's Chrome extension
to Firefox, using native browser.* API with profiler-driven
performance optimizations.

## Features
- New tab page dashboard grouped by domain
- Homepages group (Gmail, X, YouTube, etc.)
- Confetti + swoosh sound on tab close
- Duplicate detection and one-click cleanup
- Save tabs for later checklist with archive
- Dark/light theme toggle (New Feature)

## Performance
- Element pool: 128 pre-allocated confetti DOM elements
- visibility:hidden instead of card.remove() during animation
(avoids 250ms ContentWillBeRemoved style flush cascade)
- Animation fires before browser.tabs.remove() — no async delay
- Single RAF loop for all particles (was 17 separate loops)
- translate3d() GPU compositing on all animated elements
- will-change GPU hints on cards, toast, and particles
- No SVG feTurbulence noise filter (was causing full-page repaint)
- No CSS transitions on chips (removed instantly, confetti is feedback)

## Developer notes
- Firefox Manifest V3 with event-page background
- Native browser. API throughout (not chrome. shim)
- Template cloning instead of innerHTML for all rendering

## Credits
Based on the original Chrome extension by Zara
(https://github.com/zarazhangrui/tab-out)