feat: enhance options search and calendar ui

[mtskf]

Summary

Enhances the Options UI with a new search feature and significantly upgrades the DatePicker implementation.

Changes

• Options UI:
  • Implemented real-time search for snoozed tabs (keyword filtering).
  • Refined layout for Snooze Timing and Keyboard Shortcuts.
• DatePicker (Calendar):
  • Rewrote Calendar.jsx to match official Shadcn UI v9 styling.
  • Implemented custom Dropdown component for intuitive year/month navigation.
  • Replaced Popover with a centered modal overlay (bg-black/30) for better focus.
  • Fixed layout issues and hidden native select elements.
• Documentation:
  • Updated CHANGELOG, DECISIONS, and LESSONS.

Verification

• Verified build passes locally.
• Confirmed search functionality filters tabs correctly.
• Confirmed Calendar dropdowns work and match design.
• Confirmed Calendar modal opens/closes correctly.