#23300 webviews: the run board's timeline rings only its checkbox (base text-focus lint red)

Base lint red: check-text-focus-rings (part of bun run check, so the web lint (fast) job) fails on feat-cmux-next since #22408 (802f9b7aa24):

webviews/src/agent-session/acpmux/run-board/variants/timeline/timeline.css:14: `.timeline-board input:focus-visible` sets `outline: 2px solid var(--page-text-3)` on a focused text field

Change

The timeline board's only <input> is the "I reviewed this attempt" checkbox (TimelineRunBoard.tsx:546). The ring rule now names it, .timeline-board input[type="checkbox"]:focus-visible. The check still refuses rings on text fields, and the checkbox keeps its keyboard ring exactly as before.

Changelog

none

Observed / Not run

• Red on base c874b3ebf9d5 (local): python3 scripts/cmux-next/check-text-focus-rings.py (from webviews/) reports the line above.
• Green on this head: the check prints "no focus ring on a text field", and scripts/web-lint.sh passes (webviews).
• Not run: a visual check of the board's checkbox ring; the rule's declarations are unchanged and only its selector narrowed to the element it already applied to.

Agent session: huge-blue

🤖 Generated with Claude Code

---

^{Need help on this PR? Tag @codesmith-bot with what you need.}

---

Summary by cubic

Fixes the check-text-focus-rings lint failure on the run board timeline by narrowing the focus-ring selector to the checkbox instead of all inputs. The timeline board's only input is the "I reviewed this attempt" checkbox, so the keyboard ring is unchanged while web lint (fast) passes.