feat(portal-behandel): refresh the werkbak on an interval while it is open (refs #162)

`interval(WERKBAK_REFRESH_MS)` re-reads the existing BFF werkbak endpoint,
scoped to the page's lifetime with `takeUntilDestroyed()`. A background read
leaves the rows and states on screen alone until it has an answer, so a tick
neither flashes the loading state over rows being read nor swaps the list for
the failure alert on a blip — only a foreground read (on open, after a
decision) speaks for whether the werkbak is readable at all.

No new endpoint, dependency or server state: rxjs and the endpoint are both
already here (ADR-0032).

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

apps/behandel/src/app/werkbak/werkbak-page.ts

@@ -1,4 +1,6 @@
 import { Component, inject, signal } from '@angular/core';
+import { takeUntilDestroyed } from '@angular/core/rxjs-interop';
+import { interval } from 'rxjs';
 import { BffApiV1Service, type WerkbakItem } from 'api-client';
 import { UtrechtComponentsModule } from 'ui';
 
@@ -16,6 +18,11 @@ type Besluit = 'goedkeuren' | 'afwijzen';
  * Flowable `Beoordelen` tasks, read through the domain) and decides each — goedkeuren or afwijzen. A
  * decision posts to the BFF, which applies the domain transition and completes the workflow task
  * (ADR-0013; S-12). After a decision the werkbak refreshes so the handled item drops off the list.
+ *
+ * The page also re-reads itself every {@link WERKBAK_REFRESH_MS} while it is open, so a registration
+ * that reaches beoordeling after the behandelaar opened the werkbak shows up on its own — no reload
+ * (S-26/#162). Polling rather than a pushed stream: nothing notifies the BFF either, so a stream
+ * would poll the domain in the BFF instead and add connection state for the same freshness (ADR-0032).
  */
 @Component({
   selector: 'app-werkbak-page',
@@ -33,11 +40,25 @@ export class WerkbakPage {
 
   constructor() {
     this.load();
+    // ponytail: a fixed interval, polled while the page lives — it keeps refreshing in a background
+    // tab. Gate on `document.visibilityState` if the request volume ever matters.
+    interval(WERKBAK_REFRESH_MS)
+      .pipe(takeUntilDestroyed())
+      .subscribe(() => this.load({ background: true }));
   }
 
-  load(): void {
-    this.loading.set(true);
-    this.failed.set(false);
+  /**
+   * Read the werkbak. A `background` read is the interval refresh: it leaves the rows and the states
+   * the behandelaar is looking at alone until it has an answer — no loading flash on every tick, and
+   * a blip does not swap the list for the failure alert (the next tick recovers). Only a foreground
+   * read — on open, or after a decision — speaks for whether the werkbak is readable at all.
+   */
+  load(options: { background?: boolean } = {}): void {
+    const background = options.background ?? false;
+    if (!background) {
+      this.loading.set(true);
+      this.failed.set(false);
+    }
     this.bff.getBehandelWerkbak().subscribe({
       next: (rows: WerkbakItem[]) => {
         this.items.set(rows);
@@ -46,6 +67,7 @@ export class WerkbakPage {
       },
       // Surface the failure (e.g. 403 for a non-behandelaar) instead of swallowing it.
       error: () => {
+        if (background) return;
         this.items.set([]);
         this.loading.set(false);
         this.loaded.set(true);