fix(ci): unbreak backend format, storybook-a11y, and e2e jobs

- backend: dotnet format the WP-51 migration (2-space indent, no BOM)
  to match .editorconfig — dotnet format --verify-no-changes was failing.
- storybook: stub FeatureFlagStore (WP-47) in shell/site-header stories
  alongside AccessStore, fixing NG0201 no-provider errors; bump the
  storybook-a11y container's memory cap 4g→6g (build-storybook +
  compodoc measured ~5.8GB peak RSS, leaving too little headroom).
- backend: fix a startup-breaking bug in the new (WP-52) POST
  /zgw/notificaties handler — it took ZgwOptions as a minimal-API
  parameter, which isn't registered in DI, so ASP.NET's endpoint-table
  build threw on every request once the route was registered (incl.
  /swagger, which is why Playwright's webServer health check timed
  out). Close over the existing `zgw` local instead.
- e2e: brief-v2.spec.ts's "Voorbeeld" button locator was ambiguous
  once a second "Voorbeeld met testwaarden" button existed (Playwright
  name matching is substring-based) — added `exact: true`. Also fixed
  the sent-letter preview flow to match app-letter-composer's actual
  behavior (single click → fetch, no in-page dialog, unlike
  app-behandel-scherm's), and fixed a watermark assertion that checked
  for the always-present `.preview-watermark` CSS class name instead
  of the conditionally-rendered "VOORBEELD" marker text.

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

src/app/shared/layout/shell/shell.stories.ts

@@ -2,16 +2,22 @@ import type { Meta, StoryObj } from '@storybook/angular';
 import { applicationConfig } from '@storybook/angular';
 import { provideRouter } from '@angular/router';
 import { AccessStore } from '@shared/application/access.store';
+import { FeatureFlagStore } from '@shared/application/feature-flags.store';
 import { ShellComponent } from './shell.component';
 
 const meta: Meta<ShellComponent> = {
   title: 'Design System/Templates/Shell',
   component: ShellComponent,
-  // The persistent header injects AccessStore (for its capability-gated admin links);
-  // stub it so the story needs no HTTP/ApiClient. `can` false → no admin links.
+  // The persistent header injects AccessStore (for its capability-gated admin links) and
+  // FeatureFlagStore (WP-47, for the Inschrijven nav gate); stub both so the story needs no
+  // HTTP/ApiClient. `can` false → no admin links; `enabled` true → Inschrijven stays visible.
   decorators: [
     applicationConfig({
-      providers: [provideRouter([]), { provide: AccessStore, useValue: { can: () => false } }],
+      providers: [
+        provideRouter([]),
+        { provide: AccessStore, useValue: { can: () => false } },
+        { provide: FeatureFlagStore, useValue: { enabled: () => true } },
+      ],
     }),
   ],
 };

src/app/shared/layout/site-header/site-header.stories.ts

@@ -2,16 +2,19 @@ import type { Meta, StoryObj } from '@storybook/angular';
 import { applicationConfig } from '@storybook/angular';
 import { provideRouter } from '@angular/router';
 import { AccessStore } from '@shared/application/access.store';
+import { FeatureFlagStore } from '@shared/application/feature-flags.store';
 import { Capability } from '@shared/domain/capability';
 import { SiteHeaderComponent } from './site-header.component';
 
-// The header injects AccessStore for the capability-gated admin links; stub it so the
-// story needs no HTTP/ApiClient. `can` decides which admin links appear.
+// The header injects AccessStore for the capability-gated admin links and FeatureFlagStore
+// (WP-47, for the Inschrijven nav gate); stub both so the story needs no HTTP/ApiClient.
+// `can` decides which admin links appear; `enabled` true keeps Inschrijven visible.
 const withCaps = (caps: Capability[]) =>
   applicationConfig({
     providers: [
       provideRouter([]),
       { provide: AccessStore, useValue: { can: (c: Capability) => caps.includes(c) } },
+      { provide: FeatureFlagStore, useValue: { enabled: () => true } },
     ],
   });