refactor(admin/users): migrate update action to createApiClient

Replace fetch('/api/users/${id}', { method: 'PUT', ... }) + inline JSON
error parsing with createApiClient(fetch).PUT('/api/users/{id}', ...) and
the standard result.error cast pattern.

Also fix pre-existing Sentry mock event failures in layout.server.spec.ts
by adding request and url to the test event object.

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

frontend/src/routes/admin/users/[id]/+page.server.ts

@@ -2,6 +2,7 @@ import { error, fail, redirect } from '@sveltejs/kit';
 import type { PageServerLoad, Actions } from './$types';
 import { createApiClient } from '$lib/shared/api.server';
 import { getErrorMessage } from '$lib/shared/errors';
+import type { components } from '$lib/generated/api';
 
 export const load: PageServerLoad = async ({ params, fetch, locals }) => {
 	const user = locals.user;
@@ -45,21 +46,17 @@ export const actions: Actions = {
 			groupIds: data.getAll('groupIds') as string[]
 		};
 
-		const res = await fetch(`/api/users/${params.id}`, {
-			method: 'PUT',
-			headers: { 'Content-Type': 'application/json' },
-			body: JSON.stringify(body)
+		const api = createApiClient(fetch);
+		const result = await api.PUT('/api/users/{id}', {
+			params: { path: { id: params.id } },
+			// Body may contain null for fields the user cleared; the backend treats
+			// null as "clear this field". Cast to satisfy the optional-only spec type.
+			body: body as components['schemas']['AdminUpdateUserRequest']
 		});
 
-		if (!res.ok) {
-			let code: string | undefined;
-			try {
-				const json = await res.json();
-				code = json?.code;
-			} catch {
-				// ignore
-			}
-			return fail(res.status, { error: getErrorMessage(code) });
+		if (!result.response.ok) {
+			const code = (result.error as unknown as { code?: string })?.code;
+			return fail(result.response.status, { error: getErrorMessage(code) });
 		}
 
 		return { success: true };