feat(ui): accessibility pass — WCAG 2.2 AA for login/lobby/shell (F2)

Add the a11y foundation and bring login, lobby, and the in-game shell to
WCAG 2.2 AA:

- Primitives: .sr-only + .skip-link (base.css), trapFocus (modal focus
  trap + restore) and restoreFocus (menu focus restore) actions, the
  --color-focus visible ring.
- In-game shell: skip link + focusable main landmark; WAI-ARIA sidebar
  tabs (roving tabindex, arrow/Home/End, tabpanel wiring); menu Escape +
  focus restore (account / view / turn-navigator / map-toggles /
  bottom-tabs); mail compose as a role=dialog modal with a focus trap.
- login / lobby / lobby-create: skip link + main landmark, field labels,
  role=alert / role=status live regions.
- Map canvas: aria-label naming it a visual overview, with its data
  reachable by keyboard via the sidebar inspector and tables (accessible
  alternative; in-canvas keyboard nav deferred).

Gates (chromium-desktop): tests/e2e/a11y-axe.spec.ts scans every
top-level view for WCAG 2.2 AA violations (zero); a11y-keyboard.spec.ts
covers the skip link, menu Escape+restore, and tab roving. Adds
@axe-core/playwright. Docs: ui/docs/a11y.md (+ index). Marks F1 and F2
done in ui/PLAN-finalize.md.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

ui/PLAN-finalize.md

@@ -19,7 +19,15 @@ being marked done.
 
 ---
 
-## F1 — Visual design system
+## F1 — Visual design system — done
+
+Merged to `development` via PR #26 (2026-05-22): a shared design-token
+system (`ui/frontend/src/lib/theme/`), light/dark theming with a picker
+and pre-paint guard, and the whole UI migrated onto the tokens.
+Documented literal exceptions: the battle-scene data-viz palette, overlay
+scrims, and directional/deliberate drop shadows. The default theme is
+dark; flipping it to `system` is an available follow-up. Tokens and
+conventions live in `ui/docs/design-system.md`.
 
 Goal: replace the ad-hoc per-component styling (inline hex colors like
 `#0a0e1a`, one-off spacing) with a shared design language so every view
@@ -36,7 +44,17 @@ Acceptance: no literal theme colors left in component `<style>` blocks
 (spot-checked); a single token change restyles the app coherently.
 Consider the `frontend-design` skill for the palette/spacing pass.
 
-## F2 — Accessibility (WCAG 2.2 AA)
+## F2 — Accessibility (WCAG 2.2 AA) — done
+
+Shared a11y primitives (`.sr-only`, `.skip-link`, `trapFocus`,
+`restoreFocus`, the `--color-focus` ring), keyboard paths and ARIA across
+login / lobby / in-game shell (skip links + landmarks, WAI-ARIA sidebar
+tabs with roving + arrow keys, menu Escape + focus restore, the mail
+compose modal dialog with a focus trap), and the map canvas handled as a
+labelled accessible-alternative surface (data via the sidebar/tables).
+Gated by `tests/e2e/a11y-axe.spec.ts` (axe WCAG 2.2 AA scan of every
+top-level view, chromium-desktop, zero violations) and
+`tests/e2e/a11y-keyboard.spec.ts`. Documented in `ui/docs/a11y.md`.
 
 (From Phase 35.) Goal: the whole client is usable by keyboard and
 assistive tech.