refactor(api): parsePositiveIntParam fuer view-endpoint

Code-Review-Finding zu commit 82d4348: das Sibling-Endpoint
recipes/[id]/+server.ts nutzt schon parsePositiveIntParam aus
api-helpers.ts. Der neue View-Endpoint hatte die Logik inline
nachgebaut — jetzt aufgeraeumt fuer Konsistenz.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/routes/api/recipes/[id]/view/+server.ts

@@ -2,7 +2,7 @@ import type { RequestHandler } from './$types';
 import { z } from 'zod';
 import { error } from '@sveltejs/kit';
 import { getDb } from '$lib/server/db';
-import { validateBody } from '$lib/server/api-helpers';
+import { validateBody, parsePositiveIntParam } from '$lib/server/api-helpers';
 import { recordView } from '$lib/server/recipes/views';
 
 const Schema = z.object({
@@ -10,10 +10,7 @@ const Schema = z.object({
 });
 
 export const POST: RequestHandler = async ({ params, request }) => {
-  const recipeId = Number(params.id);
-  if (!Number.isInteger(recipeId) || recipeId <= 0) {
-    error(400, { message: 'Invalid recipe id' });
-  }
+  const recipeId = parsePositiveIntParam(params.id, 'id');
   const body = validateBody(await request.json().catch(() => null), Schema);
 
   try {