Adopt Selector in search-and-add — role=radiogroup containing zero radios #110

apps/search-and-add/src/ProviderPalette.svelte:29 declares <div class="saa-palette" role="radiogroup" aria-label="Search provider"> whose children are plain <button>s. A radio group with zero radios — the worst of the nine surfaces in the plan, because a screen reader announces it as a structurally broken widget rather than as a widget with a missing keyboard.

Also: selection is carried by class:active alone, so it is invisible to assistive tech; unavailable providers are dimmed with opacity: 0.35; there is no roving tabindex (N tab stops) and no arrow-key handling.

Judgement to be recorded on the issue: it is not a form value (no form, no name, no submit) and the auto entry is a behavioural default rather than a value, so real radios are the wrong fix. It has a selected state, so it is a listbox — a horizontal one.

Plan: https://github.com/lossless-group/augment-it/blob/rebuild/turbo-rsbuild/context-v/plans/Build-Selector-And-Close-The-Keyboard-Contract.md
Loop: https://github.com/lossless-group/augment-it/blob/rebuild/turbo-rsbuild/context-v/loops/Adopt-Selector-In-One-Member.md