Improve account run strip scrolling

[yvette-carlisle]

Summary

• replace the account run-chip horizontal strip with a hidden-scrollbar AppKit-backed scroller
• add edge fade, lightweight chevron controls, drag scrolling, and left/right keyboard support

Verification

• swift test --package-path apps/decodex-app
• apps/decodex-app/script/build_and_run.sh --verify
• cargo make test-decodex-app-stage
• git diff --check