Name the columns the Timing screen was already drawing

[jerome-queck]

Closes #70.

Twenty-five columns of figures and not one of them named on screen. A viewer could not tell Gap
from Interval, Last from Best, or which of the three Best columns belonged to which sector.

The design system had specified the header all along. web/design-system/timing-screen.html:58
defines .driver-row-header with all twenty-five labels, and
web/design-system/components/driver-row/driver-row.css already lays it on the same grid track
list as the rows — with header cells wearing the class of the column beneath, so a label cannot
drift from the figures it names. The application simply never rendered it: neither
web/timing-screen.ts nor web/index.html contained the string header. This carries it across,
which is the direction ADR-0010 asks changes to travel.

Decisions worth naming

• The labels are one list, beside the rows that fill those columns. A static block in
  index.html would have been twenty-five strings in a second file, free to drift from the markup
  they name.
• The header is the table's first child, as the design system lays it out. That is also what
  the row striping counts from (.driver-row:nth-child(even)), so the application's striping now
  matches the design system's reference rather than differing from it by one.
• It carries no data-driver, so a click on it opens nobody by construction rather than by a
  guard in main.ts.

Tests

The existing test asserted column order — "Gap sits left of Interval, in the order the header
names the columns" — while no header existed to name them. It now also asserts that the header is
rendered, that it has a cell for every cell a row has, that the labels most easily confused are
present, and that clicking it opens nobody. One cell short and every label right of the gap names
the wrong column while looking perfectly plausible, so the count is the assertion that matters.

test/run, npm run typecheck and shellcheck are green, and it was checked in a browser against
the backfilled Zandvoort 2026 Practice 1 with twenty-two Drivers on screen.

Not in scope

The issue asked that the header stay put when the field scrolls. The screen does not scroll: the
density budget puts the whole field on one --screen-height: 1300px screen, which is the product's
premise. Adding position: sticky would have been building for a case the design excludes. Worth
revisiting only if the field ever outgrows the screen.

Assisted-by: Claude Opus 5 (reasoning: high)
Co-authored-by: Claude noreply@anthropic.com