refactor(api): alle handler auf api-helpers umstellen

13 +server.ts handler nutzen jetzt parsePositiveIntParam und
validateBody statt jeweils lokaler parseId/safeParse-Bloecke.

Konsequenzen:
- 9 lokale parseId/parsePositiveInt Definitionen geloescht
- 11 safeParse + manueller error()-Throws ersetzt
- domains/[id], domains, profiles: catch-Block reicht jetzt HttpError
  durch (isHttpError) — vorher wurde ein 404 vom updateDomain als 409
  re-emittiert
- recipes/[id]/image: kein function-clutter mehr neben den FormData-Pfaden
- Konsistente Error-Bodies: validateBody schickt {message, issues},
  parsePositiveIntParam {message: 'Missing X' / 'Invalid X'}

Findings aus REVIEW-2026-04-18.md (Refactor A) und redundancy.md

src/routes/api/profiles/[id]/+server.ts

@@ -1,28 +1,21 @@
 import type { RequestHandler } from './$types';
-import { json, error } from '@sveltejs/kit';
+import { json } from '@sveltejs/kit';
 import { z } from 'zod';
 import { getDb } from '$lib/server/db';
+import { parsePositiveIntParam, validateBody } from '$lib/server/api-helpers';
 import { deleteProfile, renameProfile } from '$lib/server/profiles/repository';
 
 const RenameSchema = z.object({ name: z.string().min(1).max(50) });
 
-function parseId(raw: string): number {
-  const id = Number(raw);
-  if (!Number.isInteger(id) || id <= 0) error(400, { message: 'Invalid id' });
-  return id;
-}
-
 export const PATCH: RequestHandler = async ({ params, request }) => {
-  const id = parseId(params.id!);
-  const body = await request.json().catch(() => null);
-  const parsed = RenameSchema.safeParse(body);
-  if (!parsed.success) error(400, { message: 'Invalid body' });
-  renameProfile(getDb(), id, parsed.data.name);
+  const id = parsePositiveIntParam(params.id, 'id');
+  const data = validateBody(await request.json().catch(() => null), RenameSchema);
+  renameProfile(getDb(), id, data.name);
   return json({ ok: true });
 };
 
 export const DELETE: RequestHandler = async ({ params }) => {
-  const id = parseId(params.id!);
+  const id = parsePositiveIntParam(params.id, 'id');
   deleteProfile(getDb(), id);
   return json({ ok: true });
 };