Restyle tabs and option groups

[enaboapps]

Closes #885. Stacked on #894, tracked in #891.

What changed

• Tab bars are a single row. Tabs split the width equally, and long labels wrap inside their own tab, so Settings' Updates tab no longer sits alone on a second line.
• The selected tab has a brand underline and bolder text instead of a filled box. Under forced colours it gets a 4px Highlight border instead of the shadow underline.
• Tab focus uses an inset ring, which sits within the tab above the shared underline.
• Tab bars no longer reuse the option-group class. The roving tab stop, arrow keys, Home and End, and the attention marker are unchanged.
• Selected option-group and setup choices fill with the brand container, bolden, and carry a tick drawn with borders. The tick has empty content, so it is not added to the button's accessible name. It gives a shape cue that is distinct from the blue focus ring.
• Five-option groups use narrower minimum columns so they wrap less.

Validation

On this head:

• npm run lint passed
• npm test passed: 238 Vitest tests and 5 Node tests
• npm run build passed
• cargo fmt --check, cargo clippy --all-targets -D warnings and cargo test passed (566 tests, 1 ignored). No Rust changes in this stack.
• Rendered every Settings tab, Mouse with its sections open, and Scanning's Point settings in headless Chrome at 920px and 620px, light and dark.

Review follow-up

An independent review of this layer's head raised these points, now addressed:

• Tabs split the row equally and wrap long labels inside themselves. Before this, the row scrolled, and between roughly 800px and 890px wide it hid the Updates tab and its failure marker. The row wraps only when single words can't fit.
• Tabs keep one weight so neighbours don't shift. Unselected choices get their hover state back.
• A re-review found that the 64px tab minimum overrode word width, so a long word could spill out of its tab at high zoom. Tabs now never shrink below their longest word. It also found the restored hover applied to disabled choices, and hover is now limited to enabled choices outside disabled groups. Checked at 310px wide, the 620px window at 200% zoom.

🤖 Generated with Claude Code

Rebase validation (2026-09-25)

Rebased onto current main (7fb8fce, including #881) in stack order. git range-diff shows every commit in this PR is patch-equivalent to its previous head, and the intended parent remains its PR base. On the final stack tip (40c75cc), Node 24.19.0 lint, tests and build passed; Rust 1.97.1 format check, Clippy and tests passed. An independent review of the updated PR heads found no actionable findings. CI is rerunning on each new head.