Add disco mode for attendance grid v1.6.0

• Rainbow animation on attendance calendar cells with staggered delays
• Toggle in popup under new Fun section, persisted in storage
• Strips inline styles for animation, restores on toggle off
• Reacts to storage changes for cross-context toggling

Remove unused activeTab permission, fix store rejection v1.5.1

Reactive UI, inline date filter, card dismiss buttons v1.5.0
- Fetch all course grades once, re-filter and re-render reactively
on storage changes (no page refresh needed)
- Move date filter controls from popup into the dashboard widget header
- Add dismiss (×) button on course cards: visible on card hover,
turns red on button hover, hides the course via storage
- Both popup toggles and widget dismiss write to the same storage key,
changes reflect instantly in the widget via chrome.storage.onChanged

Redesign popup, editable date cutoff, CI pipeline v1.4.0
- Modern popup UI with toggle switches, header bar, GitHub link
- Date cutoff is now user-configurable via date picker
- GitHub Actions CI to build Chrome/Firefox zips on push
- Add sms-grades-firefox/ to gitignore
- Fix Firefox strict_min_version warning (128 → 140)

Added option to filter grades by semester in the settings.