Sprint: pbi-55 (#156)

* ST-cmovs79lt: Schema + migratie PushSubscription model

Voeg PushSubscription model toe aan prisma/schema.prisma met
snake_case-conventie, relation field op User, en bijbehorende
migratie (push_subscriptions tabel, FK + index op user_id).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

* ST-cmovs7e3o: web-push dependency + VAPID env vars feature-gated

Voeg web-push + @types/web-push toe aan package.json.
Registreer NEXT_PUBLIC_VAPID_PUBLIC_KEY, VAPID_PRIVATE_KEY,
VAPID_SUBJECT en INTERNAL_PUSH_SECRET als .optional() in lib/env.ts.
Documenteer alle vier in .env.example en README.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

* ST-cmovs7jgr: lib/push-server.ts met sendPushToUser + stale-cleanup

Server-only push-lib met VAPID feature-gate, send naar alle
subscriptions van een user, en automatische cleanup bij 404/410.
Unit tests: success-pad, 410 verwijdert sub, 404 verwijdert sub,
andere errors loggen zonder delete.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

* ST-cmovs7ouz: lib/push-client.ts client-side push helpers + stub actions/push.ts

Client-side helpers: isPushSupported, isIOSSafari, isStandalonePWA,
urlBase64ToUint8Array, subscribeToPush, unsubscribeFromPush.
Stub actions/push.ts zodat imports resolven (implementatie volgt
in volgende taak). Unit tests voor urlBase64ToUint8Array.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

* ST-cmovs7ut4: actions/push.ts subscribeToPushAction + unsubscribeFromPushAction

Vervangt stub met volledige implementatie: requireUser via getSession,
demo-block, Zod-validatie, upsert met user_id-scoping en user-scoped
deleteMany. Tests (8): idempotentie, demo-block, unauthenticated, invalid input.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

* ST-cmovs80c1: POST /api/internal/push/send met constant-time Bearer check

Route: 503 als INTERNAL_PUSH_SECRET uitstaat, 401 bij verkeerd secret
(timingSafeEqual), 400 bij invalid JSON, 422 bij Zod-fout, 204 bij succes.
push-server.ts: env-import vervangen door process.env om SESSION_SECRET
validatie tijdens build te omzeilen. Tests aangepast.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

* ST-cmovs862j: Admin test-send route + public/sw.js service worker

POST /api/internal/push/test-send: requireAdmin check (redirect bij
niet-admin), optioneel body met defaults, roept sendPushToUser aan, 204.
public/sw.js: push-handler met showNotification, notificationclick met
same-origin guard, focus bestaand venster of openWindow.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

* ST-cmovs8jvq: PushToggle component met 3 states + iOS-banner

Client component met states loading/unsupported/ios-needs-install/
denied/subscribed/unsubscribed. useEffect detecteert initial status,
permission-prompt alleen via user-click. iOS-banner NL, denied-uitleg,
subscribe/unsubscribe knoppen met sonner-toasts.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

* ST-cmovs8psg: notifications-sheet + iOS meta-tags in layout

notifications-sheet.tsx: PushToggle onderin met sectie
'Notificatie-instellingen' en visuele scheidslijn.
app/layout.tsx: appleWebApp.capable, statusBarStyle en
mobile-web-app-capable meta-tags toegevoegd via Next.js Metadata API.
manifest.json had al display: standalone.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

* ST-cmovs8vxj: docs/patterns/web-push.md pattern-documentatie

Architectuur-diagram, payload-shape, foutcodes, VAPID-config,
iOS-quirks, demo-users blokkade, trigger-voorbeelden (server +
HTTP) en admin-testroute curl-voorbeeld.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

---------

Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

lib/push-client.ts

@@ -0,0 +1,50 @@
+import { subscribeToPushAction, unsubscribeFromPushAction } from '@/actions/push'
+
+export function isPushSupported(): boolean {
+  return typeof window !== 'undefined' &&
+    'serviceWorker' in navigator &&
+    'PushManager' in window
+}
+
+export function isIOSSafari(): boolean {
+  if (typeof window === 'undefined') return false
+  const ua = navigator.userAgent
+  return /iPhone|iPad/.test(ua) && !/CriOS|FxiOS/.test(ua)
+}
+
+export function isStandalonePWA(): boolean {
+  if (typeof window === 'undefined') return false
+  return (
+    window.matchMedia('(display-mode: standalone)').matches ||
+    !!(navigator as Navigator & { standalone?: boolean }).standalone
+  )
+}
+
+export function urlBase64ToUint8Array(base64: string): Uint8Array<ArrayBuffer> {
+  const padding = '='.repeat((4 - (base64.length % 4)) % 4)
+  const base64Std = (base64 + padding).replace(/-/g, '+').replace(/_/g, '/')
+  const rawData = atob(base64Std)
+  const buf = new Uint8Array(rawData.length)
+  for (let i = 0; i < rawData.length; i++) buf[i] = rawData.charCodeAt(i)
+  return buf
+}
+
+export async function subscribeToPush(publicKey: string): Promise<PushSubscription> {
+  const reg = await navigator.serviceWorker.register('/sw.js', { updateViaCache: 'none' })
+  await navigator.serviceWorker.ready
+  const sub = await reg.pushManager.subscribe({
+    userVisibleOnly: true,
+    applicationServerKey: urlBase64ToUint8Array(publicKey),
+  })
+  await subscribeToPushAction(sub.toJSON() as Parameters<typeof subscribeToPushAction>[0])
+  return sub
+}
+
+export async function unsubscribeFromPush(): Promise<void> {
+  const reg = await navigator.serviceWorker.getRegistration()
+  const sub = await reg?.pushManager.getSubscription()
+  if (sub) {
+    await sub.unsubscribe()
+    await unsubscribeFromPushAction({ endpoint: sub.endpoint })
+  }
+}