feat(fp): WP-17 — app-level a11y: route focus, template lint, WCAG checklist

Adds route-change focus management (new page's h1, afterNextRender) plus
scroll-position restoration wired once in app.config.ts; angular-eslint's
templateAccessibility bundle linting every inline template via
processInlineTemplates (verified firing with a planted violation, one real
hit fixed in rich-text-editor); docs/wcag-checklist.md and Foundations/
Accessibility MDX tying the four a11y layers (axe, lint, play tests,
manual checklist) together. The checklist pass already earned its keep —
it found a real 320px overflow in aanvraag-block's warning alert.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/docs/a11y.mdx

@@ -0,0 +1,69 @@
+import { Meta, Canvas } from '@storybook/addon-docs/blocks';
+import * as AlertStories from '../app/shared/ui/alert/alert.stories';
+import * as FormFieldStories from '../app/shared/ui/form-field/form-field.stories';
+
+<Meta title="Foundations/Accessibility" />
+
+# Accessibility
+
+No single tool catches every a11y class of bug, so this repo layers four, each catching
+what the ones below/above it can't.
+
+## The layers
+
+1. **Axe on every story** (WP-01) — `@storybook/addon-a11y` in the panel, plus
+   `@storybook/test-runner` + `axe-playwright` gating CI (`npm run test-storybook:ci`).
+   Catches structural/contrast/ARIA-shape violations on every component, automatically,
+   as soon as a story exists. Escape hatch: `parameters: { a11y: { disable: true } }`,
+   only with an inline justification comment + a cross-reference to the WP that will fix
+   it (see e.g. `task-list.stories.ts`).
+2. **Template a11y lint** (WP-17) — `angular-eslint`'s `templateAccessibility` config
+   (`alt-text`, `label-has-associated-control`, `click`/`mouse-events-have-key-events`,
+   `interactive-supports-focus`, `valid-aria`, `no-autofocus`, …) running on every inline
+   template via `angular.processInlineTemplates` (this repo has no `.html` files — every
+   template is a string in the `@Component` decorator; the processor extracts each one
+   into a virtual file the template rules can lint). Catches missing alt text, unlabelled
+   controls, and interactive elements that can't be reached by keyboard — at lint time,
+   before a story even exists.
+3. **Play tests** (WP-16) — Storybook stories assert the wiring axe/lint can't see:
+   `form-field.stories.ts`'s canonical composition asserts `aria-describedby` joins
+   `-desc`/`-error` in the right order; `alert.stories.ts` asserts `role="alert"` for
+   errors vs `role="status"` for info/ok/warning. These run as part of the same
+   `test-storybook:ci` gate as the axe checks, so a regression fails CI, not just a panel.
+4. **Manual WCAG checklist** (`docs/wcag-checklist.md`) — what none of the above can see:
+   tab order across a whole page, focus traps, 200%-zoom reflow, and how a real screen
+   reader narrates a flow. A living per-page checklist, not a one-time audit — it already
+   caught a real bug (a dashboard alert overflowing at 320px) that no automated layer here
+   would have flagged.
+
+## Component wiring this protects
+
+<Canvas of={FormFieldStories.WithDescriptionAndError} />
+
+The description (`-desc`) and error (`-error`) ids are joined in a pinned order so a
+screen reader announces the hint, then the error, never neither. See
+`text-input.component.ts`'s `describedBy()`.
+
+<Canvas of={AlertStories.Error} />
+
+Errors are `role="alert"` (assertive — interrupts, because the user needs to know
+*now*); info/ok/warning stay `role="status"` (polite) so they don't interrupt whatever
+the user is doing. See `alert.component.ts`.
+
+## Route-change focus
+
+Client-side routing has no page (re)load, so a screen reader/keyboard user's focus stays
+wherever it was — usually the link they just clicked, now detached from any content that
+matters. `shared/layout/route-focus.ts` moves focus to the new page's `<h1>` (every page
+has exactly one via `page-shell`) on every navigation after the initial load, deferred via
+`afterNextRender` so it doesn't race the view-transition DOM swap. Scroll position resets
+the same way (`withInMemoryScrolling`), both wired once in `app.config.ts` — not per page.
+
+## Where the skip register lives
+
+`npm run lint` fails the build on a real template a11y violation, and `test-storybook:ci`
+fails it on a real axe violation. Both can be locally disabled — the lint rule via a
+normal ESLint disable comment, axe via `parameters: { a11y: { disable: true } }` — but
+only with a comment naming *why* and a cross-reference to the WP expected to remove the
+skip (see `docs/backlog/WP-13-cibg-gap-register.md`'s marker convention, reused here).
+Grep `a11y: { disable: true }` in `*.stories.ts` for the current list.