feat: Add basic UI, search implimentation

[JustAdumbPrsn]

Extends #12655

• Added library-item along with styling
• Search works properly and sorted by date.
• Added separator which shows Today, Yesterday, then previous days of week, then full date, i.e, 13 March 2026
• Search bar currently also has a Filter button but would probably be changed to "Sort" or "View" button like native firefox.

Note:

• Styling may need more attention to use more variables which zen tabs does.
• The history items do not currently have the recently closed tabs section, button to clear history, and glance button for each item to open that item as glance.
• The downloaded items do not currently show the download progress ring while it does show active download exactly how firefox natively does.

[mr-cheffy]

Please use something like:

new Intl.RelativeTimeFormat(undefined, {
          numeric: "auto",
        }).format(daysUntil, "day")

instead of hard coding it

[mr-cheffy]

You can now just use

library-search-placeholder =
	.placeholder = Search…

[JustAdumbPrsn]

thanks, on it