feat(fp): WP-05 — parse-don't-validate closure + MDX

Close the three remaining unvalidated `as <DomainType>` casts at the wire
boundary (intake-policy, big-register aantekening type, brief passage scope),
each replaced by a Result-returning parser with a rejection-case spec, plus
the Foundations/Parse, don't validate curriculum page.

src/app/herregistratie/infrastructure/intake-policy.adapter.ts

@@ -1,4 +1,6 @@
 import { Injectable, inject, resource } from '@angular/core';
+import { Result, ok, err } from '@shared/kernel/fp';
+import { IntakePolicy } from '@herregistratie/domain/intake.machine';
 import { ApiClient } from '@shared/infrastructure/api-client';
 
 /**
@@ -11,6 +13,21 @@ export class IntakePolicyAdapter {
   private client = inject(ApiClient);
 
   policyResource() {
-    return resource({ loader: () => this.client.policy() });
+    return resource({
+      loader: async () => {
+        const parsed = parseIntakePolicy(await this.client.policy());
+        if (!parsed.ok) throw new Error(parsed.error);
+        return parsed.value;
+      },
+    });
   }
 }
+
+/** Trust-boundary parse: an unrecognized/missing threshold is an explicit Failure. */
+export function parseIntakePolicy(json: unknown): Result<string, IntakePolicy> {
+  if (typeof json !== 'object' || json === null) return err('intake-policy: not an object');
+  const dto = json as { scholingThreshold?: unknown };
+  if (typeof dto.scholingThreshold !== 'number')
+    return err('intake-policy: missing scholingThreshold');
+  return ok({ scholingThreshold: dto.scholingThreshold });
+}