fix(web): commit slider steps reliably, scope pre sizing, measure nested labels

Three review findings:

- High: track clicks and keyboard steps fire input and change in one task,
  before any re-render, so the change handler read a stale draft and dropped
  the commit. The draft now mirrors into a ref written inside the input
  handler itself, so the commit reads the same turn's value.
- The global pre font-size rule beat text-size utilities and inherited sizes
  on unrelated pre surfaces (terminal previews, approvals). The code size is
  now scoped to chat markdown code blocks; diffs and file previews already
  take it through --diffs-font-size.
- SelectValue truncates internally, so the outer label marker's scrollWidth
  matched its clipped box and the workspace/environment labels fell out of
  the strip's overflow measurement. The text width is now the largest
  scrollWidth in the label subtree.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
5ce99c20bbWout Stiens committed on 8/1/2026, 9:47:54 AMparent805813e
3 files changedLine totals unavailable