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/app/shared/ui/rich-text-editor/rich-text-editor.component.ts

@@ -161,6 +161,7 @@ export interface PlaceholderOption {
       #editor
       class="rte-editable"
       [attr.contenteditable]="editable()"
+      [attr.tabindex]="editable() ? '0' : null"
       (input)="emit()"
       (keydown)="onKeydown($event)"
       role="textbox"