refactor: dedupe Settings segmented fieldsets into OptionGroup

[enaboapps]

Closes #684.

Stacked on #691 — base is refactor/settings-module-683, so review this after that merges (or review just the two-file diff here).

The eight segmented option fieldsets in SettingsView were hand-rolled copies of the same fieldset > legend > div.segmented > button[aria-pressed] structure. This replaces them with one OptionGroup.

Added to controls.tsx

• OptionGroup — generic over string | number option values, with an optional columns modifier (three / four / five, omitted entirely for the one group that has no column class) and a children slot for the trailing note that the overlay-visibility fieldset renders inside its fieldset.
• secondsOptions — builds the {value / 1000}s labels shared by the movement, scroll, key and dwell interval groups. Returns the label as a fragment so the button keeps its two text nodes rather than collapsing to one.
• overlayVisibilityOptions, overlaySizeOptions.

SettingsView.tsx: 82 → 70 lines.

The pointer-speed fieldset is deliberately untouched

Its buttons carry per-option aria-labels and it renders an exact-speed select plus a movement-values readout, so it is not the same structure. Folding it in would have meant changing DOM.

Byte-identical DOM — verified, not assumed

Rather than relying on the tests passing, I dumped the rendered Settings view innerHTML on the parent commit and on this one and diffed them:

State	Result
Default settings	identical
Every feature toggle enabled, non-default selections across all eight groups	identical

The second case matters because it exercises the aria-pressed and disabled states that the default dump leaves uniform. The dump harness was temporary and is not committed.

Validation

Check	Result
npm run lint	pass
npm test	pass — 75 tests, no test file changed
npm run build	pass
cargo fmt --check	exit 0
cargo clippy --all-targets -- -D warnings	exit 0
cargo test	exit 0 — 263 + 7 tests

No Rust files are touched; the Rust gates are run per AGENTS.md.

🤖 Generated with Claude Code

[enaboapps]

Superseded by the reopened PR against main — this one was auto-closed when its base branch was deleted on merge of #691.