Fix right-to-left behaviour of the card slider, live feed ticker, directional icons and letter-spacing

Problem/Motivation

The theme builds its component CSS through postcss-rtlcss and loads a right-to-left library, so most of the layout mirrors. Checked on a right-to-left translation of The Rightup, four things still behave wrongly when dir="rtl".

• The card slider's Next button does nothing and Previous never enables, because the script reads scrollLeft as positive.
• The live feed ticker is empty for most of each loop: at mid-cycle both item groups sit off-screen. A time next to a headline also renders as "PM 12:00".
• Directional icons (arrows, chevrons) keep their left-to-right direction, including the slider and pager chevrons and the View Show arrow.
• Taxonomy labels and display headings keep their letter-spacing on right-to-left text (0.8px on taxonomy labels). Joined scripts should not be tracked; Chromium already ignores it, so the visible change there is none.

Steps to reproduce

1. Install The Rightup and a right-to-left language with translated news, and open its home page in that language.
2. Press Next on the card slider, watch the ticker under the header for a full loop, and look at the chevrons and arrows.

Proposed resolution

• Card slider: handle the negative scrollLeft of right-to-left scrolling, so Next and Previous move and enable correctly.
• Live feed: mirrored keyframes in RTL so a group always covers the strip, and let the time and the title take their direction from their own text (unicode-bidi: plaintext).
• Mirror the directional icons in vartheme-rtl.base.
• Reset letter-spacing to normal for the taxonomy label and the display headings in RTL.

Left alone on purpose: the audio player's play triangle is mirrored in RTL in the source, which fits a progress bar that fills from the right. Most guidelines keep media icons unmirrored, so that is a design decision for the maintainers.

Remaining tasks

• ✅ File an issue
• ✅ Addition/Change/Update/Fix
• ❌ Testing to ensure no regression
• ❌ Automated unit/functional testing coverage
• ➖ Developer Documentation support
• ➖ User Guide Documentation support
• ➖ UX/UI designer responsibilities
• ❌ Accessibility and Readability
• ❌ Reviewed by a human
• ❌ Code review by maintainers
• ❌ Full testing and approval
• ❌ Credit contributors
• ❌ Review with the product owner
• ❌ Update Release Notes
• ❌ Release

User interface changes

• None in left-to-right. In right-to-left the slider moves, the ticker stays filled, and the icons point along the reading direction.

API changes

• N/A

Data model changes

• N/A

Release notes snippet

• None in left-to-right. In right-to-left the slider moves, the ticker stays filled, and the icons point along the reading direction.

AI-Generated: Yes. Drafted and tested with Claude Code, reviewed by the contributor.