Accessibility: hover-only tooltips, misused tablist roles, and a layout table

[jeremymanning]

Collected by an adversarial accessibility pass during feature 005. All pre-existing; none
blocks the documentation work, but each makes real information unreachable for some users.

1. Hover-only tooltips (highest impact)

Token probabilities, sphere labels and residual-norm bars are all onmousemove /
onmouseleave on role="note" elements with no tabindex:

• ArchChat.svelte (reply tokens — the per-token probability and its top-5 alternatives)
• ArchTracePanel.svelte (token chips, norm bars)
• GeoScene.svelte (sphere dot labels, pointermove)

Keyboard users cannot reach them; touch users effectively cannot either. For the reply
tokens the tooltip is the only place the alternatives appear.

Fix: tabindex="0" plus onfocus/onblur mirroring showTip/hideTip; show the sphere
label on pointerdown as well as pointermove.

2. role="tablist" on things that are not tabs

GeometryLab.svelte field/layer segmented pickers carry role="tablist" but their children
have no role="tab", no aria-selected, and there is no tabpanel. A screen reader
announces a tab list containing nothing it recognises, and the active field/layer is never
conveyed. FinetunePanel/TrainPanel/AttentionView set role="tab"/aria-selected but
still have no tabpanel, aria-controls, or arrow-key handling.

Fix: role="radiogroup" + role="radio" aria-checked, or drop the roles and use
aria-pressed on the buttons (they already behave as toggles).

3. The Info tab's notation table is a layout table

Four columns alternating symbol/definition with no <thead>/<th>. It is a glossary, so
assistive tech reads two unrelated pairs as one row.

Fix: a <dl> with display: grid; grid-template-columns: auto 1fr auto 1fr — same visuals,
correct semantics, and it collapses to two columns on a phone for free.

Already fixed in feature 005

Equation blocks and tables are now keyboard-scrollable (tabindex="0" on the scroll
container, white-space: nowrap so overflow-x actually engages); <table display:block>
no longer strips table semantics; Explain titles are exposed as headings for heading
navigation; Explain summaries wrap on narrow screens.