docs: add ADR-0016 for accessibility baseline (WCAG 2.2 AA + targeted AAA, spartan-ng + CDK + Tailwind, APF panel)

Pin the a11y baseline given the host organisation context (APF France
Handicap, where accessibility is the core mission, not a compliance
checkbox):

- Conformance: WCAG 2.2 AA universal + AAA on criteria with high
  impact for the user base (1.4.6 Enhanced Contrast 7:1, 2.2.3 No
  Timing, 2.3.3 Animation from Interactions, 3.1.5 Reading Level,
  1.4.8 Visual Presentation, 2.4.9 Link Purpose, 3.3.5 Help). RGAA 4.1
  alignment for French audit context.

- User-preferences panel as a first-class feature: contrast (3 tiers),
  text size (up to 200%), motion, text spacing, cognitive
  simplification, reading focus. Persisted in session (ADR-0010).

- UI stack: Angular CDK + spartan-ng + TailwindCSS (not Angular
  Material; not React libs). Components copy-pasted into
  libs/shared/ui under our control. Design tokens with
  contrast-verified colour pairs in libs/shared/tokens.

- Tooling and CI gates: @angular-eslint/template/* a11y rules
  (blocking), @axe-core/playwright e2e blocking on critical/serious
  violations, design-token contrast verifier (blocking), touch-target
  size check (blocking on 44x44 min, default 48x48). Wires into the
  a11y gate slot from ADR-0015.

- Manual testing: keyboard and screen reader required on every UI PR
  via PR-template checklist; APF user-panel session before every major
  release covering visual / motor / cognitive / hearing categories.

- Documentation: public accessibility statement at /accessibility (EN)
  and /accessibilite (FR) - EAA legal requirement, generated from
  source-of-truth in the repo. Internal patterns library in
  docs/accessibility/.

decisions/README.md index updated. CLAUDE.md gains an explicit
'Accessibility' line pointing to ADR-0016 and the CI/CD line is
adjusted to mark the a11y gate as locked-in (no longer 'future').

CLAUDE.md

@@ -43,7 +43,8 @@ The structural choices are recorded as ADRs and summarized below. Any change to
 - **Observability:** Pino + `nestjs-pino` for structured JSON logs, OpenTelemetry SDK + auto-instrumentations for traces, W3C Trace Context propagation across SPA → BFF → DB → Redis, `nestjs-cls` for request-scoped context (`trace_id`, `session_id`, `user_id_hash`, `audience`), 100 % sampling at the app with tail sampling deferred to the OTel Collector, stdout + OTLP shipping — see [ADR-0012](decisions/0012-observability-pino-opentelemetry.md).
 - **Audit trail:** dedicated `audit.events` schema in the same Postgres instance, append-only by Postgres role grants (`audit_writer` INSERT, `audit_reader` SELECT, `audit_archiver` DELETE older than retention; no `UPDATE`/`TRUNCATE` to anyone); 365-day retention default; cross-referenced with app logs via `trace_id` and `actor_id_hash` (same salt); blocking writes (no audit ⇒ no action) — see [ADR-0013](decisions/0013-audit-trail-separated-postgres-append-only.md).
 - **Downstream API access:** unified `DownstreamApiClient` (`@nestjs/axios` + `cockatiel`), per-service `DownstreamApiConfig`; default auth strategy is **OBO via MSAL Node** for Entra-protected APIs (downstream-scoped tokens cached in Redis with AES-256-GCM under a dedicated key); fallback strategy is service credential + signed `X-User-Assertion` JWT (BFF JWKS at `/.well-known/jwks.json`); per-call audience pre-check; no `axios`/`fetch` outside `src/downstream/` — see [ADR-0014](decisions/0014-downstream-api-access-obo-pattern.md).
-- **CI/CD:** **Gitea Actions** (level-2 implementation; will be superseded by a GitLab migration ADR within 6-18 months). Trunk-based with squash-merge, branch protection on `main`, all CI gates blocking. Thin YAML — orchestration logic lives in `package.json` scripts (`ci:check`, `ci:scan`, `ci:commits`) and Nx targets, runnable locally. Gates: format / lint / type-check / test / build / audit / secret-scan / commit-lint, plus future `a11y` and `perf`. Self-hosted `act_runner` on-prem. Conventional Commits validated locally (hook) and in CI (defense in depth). Required reviewer count = 0 in v1, raised to ≥1 once a second contributor joins. Signed commits recommended, revisited at GitLab migration — see [ADR-0015](decisions/0015-cicd-gitea-actions.md).
+- **CI/CD:** **Gitea Actions** (level-2 implementation; will be superseded by a GitLab migration ADR within 6-18 months). Trunk-based with squash-merge, branch protection on `main`, all CI gates blocking. Thin YAML — orchestration logic lives in `package.json` scripts (`ci:check`, `ci:scan`, `ci:commits`) and Nx targets, runnable locally. Gates: format / lint / type-check / test / build / audit / secret-scan / commit-lint, plus `a11y` (per ADR-0016) and future `perf`. Self-hosted `act_runner` on-prem. Conventional Commits validated locally (hook) and in CI (defense in depth). Required reviewer count = 0 in v1, raised to ≥1 once a second contributor joins. Signed commits recommended, revisited at GitLab migration — see [ADR-0015](decisions/0015-cicd-gitea-actions.md).
+- **Accessibility:** **WCAG 2.2 AA baseline + targeted AAA** on criteria with high impact for APF's user base (1.4.6 Contrast Enhanced, 2.2.3 No Timing, 2.3.3 Animation, 3.1.5 Reading Level, 1.4.8 Visual Presentation, 2.4.9 Link Purpose, 3.3.5 Help). RGAA 4.1 alignment for French audit. UI stack: **Angular CDK + spartan-ng + Tailwind** (no Angular Material; no React libs). User-preferences panel (contrast / text size / motion / spacing / cognitive simplification / reading focus) persisted in session. Tooling: `@angular-eslint/template/*` lint, `@axe-core/playwright` e2e (blocking on critical/serious), token-contrast CI check, touch-target check (44×44 min). Manual testing cadence with APF's internal user panel before each major release. Public accessibility statement page at `/accessibility` and `/accessibilite` — see [ADR-0016](decisions/0016-accessibility-baseline-wcag-aa-targeted-aaa.md).
 - **Local quality gates:** Husky + lint-staged + commitlint with Conventional Commits — see [ADR-0007](decisions/0007-pre-commit-hooks-and-conventional-commits.md).
 - **Runtime:** Node.js latest LTS major.