fix(frontend): low-severity accessibility fixes (focus, aria, target size) #729

Summary

Low-severity accessibility items from the 2026-10-08 UI review.

Where

Reviewed commit b50ca38. UX-36 verified live (axe); the others are source-level.

• UX-27: Escape in the RI-exchange filter popover drops focus to the body (the History popover handles it correctly). frontend/src/riexchange.ts:1268-1271; correct reference frontend/src/lib/history-filter-popover.ts:116-121. Related: refactor(frontend): consolidate column-filter popover plumbing into shared lib #18 (consolidation refactor; would fix it incidentally but does not mention the defect).
• UX-31: chip-select search keeps aria-activedescendant on the trigger and focus is not returned to the trigger after a pick. frontend/src/lib/chip-select.ts:181,199-204,235.
• UX-34: skeleton loaders are not announced (no aria-busy); the ladder <canvas tabindex=0> is a dead Tab stop. frontend/src/lib/skeleton.ts; frontend/src/ladder-timeline.ts:36. Related: chore(frontend): standardize loading indicators and add slow/empty fallbacks #186 (loading indicator consistency, not announcement).
• UX-36: axe: #topbar-filters has aria-label on a plain div (needs role="group"); 34 small inline links on Admin General fail target-size. frontend/src/index.html:42.

Failure scenario

Keyboard users lose their place after Escape or a chip pick; screen-reader users get no loading announcement and a Tab stop with no action; the global filter label is ignored by assistive tech.

User impact

Keyboard and screen-reader users on RI exchange, filters, the ladder and Admin General.

Suggested fix

Return focus to the trigger on Escape and after a pick; set aria-busy on skeleton containers; remove tabindex from the canvas (or give it a keyboard action); add role="group" to #topbar-filters; enlarge inline link targets.

Screenshots

In the review fleet archive (/Users/cristi/.claude/agent-comms/review-fleet-20261008/screens/), NOT uploaded: usab-th-filter-enter.png (focus falls to body in a filter header, related), usab-admin-general.png (UX-36). Others: none (source-level).

Severity

Low: WCAG gaps with workarounds; axe rates two of them serious but they are minor structural issues.

Reviewer IDs: UX-27 (usab L2), UX-31 (usab L6), UX-34 (usab L13), UX-36 (usab L15)
Found by the 2026-10-08 review fleet.