a11y(backend): keyboardable matrix, qualified actions, live toasts (#2343 #2344 #2351)

[kpoineal]

Summary

Three NVDA/keyboard accessibility fixes in BackendManager.tsx (Group C of the gui3 a11y series).

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#2343 — Backend matrix cells are now keyboard-operable

Problem: Clickable <div> cells in the capability matrix had no keyboard focus, no ARIA role, and no selected state — mouse-only.

Fix: Applied the overlay-button pattern (same as recipe-card__overlay-btn in PresetManager):

• .cell--selectable gains position: relative.
• A <button class="cell__select-btn" aria-pressed aria-label> with position: absolute; inset: 0; z-index: 0 covers the full cell.
• aria-pressed reflects selection state ("true"/"false").
• aria-label includes the human-readable recipe label and backend identifier (e.g., "llama.cpp (vulkan), Available").
• Action buttons (.cell__actions) get position: relative; z-index: 1 so they remain clickable above the overlay.
• The global :focus-visible ring (2px accent outline) renders on the overlay button when keyboard-focused.

Closes #2343

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#2344 — Backend action buttons now have qualified accessible names

Problem: Install, Update, Uninstall buttons had generic labels ("Install" / "Update" / "Uninstall") that collided across multiple backends when announced by NVDA.

Fix: Added aria-label to each action button containing both the recipe label and backend identifier:

• aria-label="Install llama.cpp (vulkan)"
• aria-label="Update llama.cpp (vulkan)"
• aria-label="Uninstall llama.cpp (cpu)"
• aria-label="Setup guide for ryzenai (hybrid)"

Visible button text is unchanged; aria-label overrides the accessible name for AT.

Closes #2344

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#2351 — Toast and preset notices are now live regions

Problem: backends__toast and context-rail__notice were conditionally mounted ({msg && <div>…</div>}). Mounting a node with content does not trigger NVDA live region announcements — the element must already exist in the DOM before content changes.

Fix: Two always-present <div role="status" aria-live="polite" aria-atomic="true" class="sr-only"> elements added:

• data-backends-toast-live — mirrors toastMsg (installing/updating/uninstalling progress and completion).
• data-backends-preset-notice-live — mirrors presetNotice (preset assignment confirmations and incompatibility notices).

Visual toast and notice remain conditionally rendered (no visual change). Only the sr-only live regions are always in the DOM.

Closes #2351

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Tests

8 new tests added to tests/a11y.spec.ts (A35–A42):

• A35–A38: matrix cell button existence, toggle, focusability, label qualification
• A39–A40: Install/Uninstall button qualified aria-label
• A41–A42: toast and preset-notice live region attributes

Result: 58 passed / 7 skipped / 0 failed (baseline was 50 passed / 7 skipped / 0 failed)

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A human reviews before merge. No behavior or visual changes for mouse/pointer users.

[kpoineal]

Internal review: LGTM (advisory — human approval required)

Authored by Mattingly; reviewed by Lovell.

• BackendManager.tsx ~line 739 — overlay button (a11y: Backend matrix cells are mouse-first #2343): cell__select-btn at position: absolute; inset: 0; z-index: 0 with action buttons at z-index: 1 is the established pattern (mirrors recipe-card__overlay-btn in PresetManager). aria-pressed for selection state is correct; aria-label includes recipe label + backend identifier + badge text — sufficient for NVDA disambiguation. position: relative added to .cell--selectable in styles.css. ✅
• Action button labels (a11y: Backend action buttons are generic #2344): Install/Update/Uninstall/Setup guide for () — qualified, consistent format. Visible text unchanged. ✅
• Live regions (a11y: Backend/preset toasts and notices are not consistently live regions #2351): Always-present role="status" aria-live="polite" aria-atomic="true" .sr-only pattern is correct — conditional mounting does not trigger NVDA, content mutation on already-mounted element does. Two separate regions (toast, preset notice) in different DOM positions; simultaneous updates are an edge case the pattern handles acceptably. ✅
• Tests A35–A42: A36 (toggle aria-pressed true→false→true) is the critical behavioral assertion. A41/A42 verify presence and attributes of both live regions. Solid coverage.
• Minor: if a future recipe type has no entry in RECIPE_LABELS, the raw recipe ID surfaces in the aria-label — acceptable fallback, not a bug.

[kpoineal]

Rebased onto merged base a8718a7. Conflicts resolved in ests/a11y.spec.ts (branch's new tests renumbered to A51–A58) and ACCESSIBILITY.md (union merge). Final suite: 69 passed / 7 skipped / 0 failed. — Mattingly

[fl0rianr]

LGTM